My response from the perspective of my Energy Weapons NCR character:

Use energy weapons all the way! If you know where to look (and take out those damn VanGraffs) you'll never run out of ammo.

Always use the Laser Rifle, with the focus optics and the beam spilter, but not the scope, I kill deathclaws by the dozens with my laser rifle.

Caesar's Legion? The bunch of man-skirt wearing savages? They dont even know how to respect women! I kill their assassins all day long without a scratch on me (the key is to use ranged weapons, the group of idiots uses mostly melee)

Also, yes, have fun. Or I will find you.
I higly suggest atleast one playthrough with Wild Wasteland, ever since my first playthrough with it, I have never gone back.

Giant radscorpions are some of the most dangerous creatures for a low-level character.

Their main strength is high DT (they will negate 80% of your damage if your weapon's DAM is under 18), speed and the ability to cripple your limbs very often.

How to fight: armor-piercing rounds and DT-ignoring weapons work best. Failing that, go for weapons with highest possible DAM.

How to fight at low level: I've been known to take down up to two Giant Radscorpions with the 9mm SMG. The tricks is to run backwards and shoot at them until they fall and be quick enough to inject yourself with stimpacks as you go. Try to target the claws; they seem to be more vulnerable than the rest of that armored thing, and crippling limbs stuns the scorp for a short while, giving you some breathing room.

Explosives make short work of GRS and cripple limbs very quickly, so if you have Courier's stash, that would be a good time to use Mercenary's Grenade Rifle. Another good trick is to make some Satchel Charges or collect some of those Powder Charges that the Powder Gangers place around their camps, set up a mined trail and lure the scorpion to run through it. Their AI is dumb as a brick, they'll just chase you in a straight line and trigger any charge they run into.

GRS hard points: The legs(50% DR). GRS has no weak points, it sustains equal limb damage to the tail, torso, and claws. That said, it's a lot easier to to hit the claws than the others when it's charging at you! HP rounds also work...well, not wonders, but somewhat better than standard 9mm bullets against GRS as long as you aren't using Maria.

And yes they are! I got killed by one at level 1 on my first playthrough. It spawned IN Goodsprings Cemetery. Scared the crap outta me. The tell-tale sign of rocks and desert sands kept me away long after Deathclaws ceased to be a threat.

I can agree with everything Golem said, just adding three strategies: 1) Sneak everywhere you go, and use this to get away from GRS before hell happens. 2) Find yourself a Caravan Shotgun and start breaking down 20 gauge buckshot and remaking them as 20 gauge slugs(about level 8, a Caravan Shotgun loaded with slugs becomes an extremely respectable anti-GRS weapon if your reflexes are good, your Guns skill high, & you take the "Shotgun Surgeon" perk. Given that you somehow beat ANY CoD game on Veteran, I think you have good reflexes and aim). 3) Take the high ground. There are locations GRS literally cannot reach you at, and they move slower traveling uphill. Failing that, position yourself under a cliff so they come running over you and you can hit them without them being able to retaliate.

-Nukeknockout

First thing to note is that New Vegas, and in essence Fallout 3, aren't your average run of the mill FPS game where you can run and gun and pretty much win all the time. Those are simple games in comparsion and in general, the Fallout's are more geared around a slower pace and a more tactical angle.
Don't expect to win against a lot of your opponents in FO3 and New Vegas by just running and gunning, you'll more than likely be killed. It's better to use the VATS often adn if you can't use it, then time your shots, keep your aim steady and if you need to - use a grenade or other explosive. If it doesn't kill them, it will at least hurt them, maybe cripple a limb.

For example running and gunning into an area filled with Deathclaws or Cazadors while having a big gun doesn't mean you'll win, the chances are you'll be ripped apart before you can kill one opponent. Strike from a distance if the chances are good, improve your stats, don't take on a lot of opponents at once without decent stats and decent weapons. The game uses a system where you may end up missing even when they're right in front of you, just as the enemy might miss you, or you might get a critcal hit just as the enemy does.
Learn how to use that system to your advantage, note your strengthes and weaknesses. Going all Rambo like in any FPS doesn't work very well in FO3 and New Vegas. Unless you love being killed a lot and loading a save often.

Tactics are a great asset, understanding RPG's - Role Playing Game, not weapon - is a great asset, being calm and patient with how you play the game is a great asset. They aren't some FPS that you'll complete in a few hours, they take a lot longer and require the player to think carefully about their actions and their intended plan as they progress.
Think tactics, be patient. Eventually you'll adapt and find yourself doing a lot better than expected.

Some of my tips for surviving the wastes:

1. If the enemy has a bigger gun than you, shoot it to disarm them and possibly break the weapon.

2. If it is a big, ugly monster try to get a sneak crit on its legs first so that they are crippled. If that fails do not be afraid to lay mines or toss grenades at their feet so that their legs are broken and you can then outrun them. You can kill any critter in the game, eventually, with any ranged weapon as long as you cripple the legs.
*in the case of cazadores shoot the wings first
**also works for melee humanoids if you fail to keep them at range

3. if you find an area that has a bunch of traps that keep killing you and you can't seem to find them, toss a grenade in their general direction so the explosion sets them off. Your mileage may very if you are a bad shot with grenades.

4. Picking 1 weapon type and repair will make early game combat MUCH easier. Being able to deal more damage with greater accuracy and keeping weapons in top shape with less effort is a godsend. Later on repair will allow you to convert ammo types you do not use into special hand-loaded rounds that kick ass.

5. If you plan on sneaking and playing sniper tag with a group of enemies, make sure to hide behind cover after every shot so there is less chance of the enemy spotting your location. *this is best done at extreme ranges (outside of VATS range)

6. if you are indoors a silenced weapon will help to prevent everyone in a building from being alerted to your presence as you fight stuff.

7. Having high perception, agility, and luck helps a lot with ranged weapons. Also, using ranged weapons that require a higher strength than your character possesses will result in a lot less accuracy.

8. Sunset Sarsaparilla is very cheap and effective at healing your wounds early on.

9. For some easy cash you can pick up weapons off fallen enemies and repair them to sell at the nearest vendor. Depending on the weapon you can increase its value by hundreds to thousands of caps.

10. If you use energy weapons try to pick up a recharger rifle and then a recharger pistol as soon as they are available. These weapons regenerate their own ammunition so they can save you a lot of money.

11. Quests net experience much faster than wandering around shooting stuff, especially early on.

12. during a shootout is always wise to duck behind cover while an enemy fires at you, then jump out and shoot while they reload. (probably obvious for an FPS vet like you though)

13. Shooting an enemy in the head has a high chance of stunning them for several seconds. Use that time to finish them off, reload, or run as necessary.


That was all I can think of off the top of my head.

Some more advice I thought of.

When fighting Jackals or Vipers, try to take out the ones with Grenade Rifles first. They are the most dangerous because they'll cripple your limbs on almost every hit.

An easy way to level up is hunting Bighorners in the mountains between Novac and Caesar's Legion Safehouse. An advlt Bighorner is worth 50 EXP, and they're easy to kill if you aim for heads. Try to not alert them off though; Bighorners have a knockdown attack, and a group of them can easily kill you with a succession of knockdowns which will prevent you from defending yourself.

Be VERY careful with Nightstalkers. If you see one, chances are the rest of the pack isn't far behind, and being ambushed by a pack of Nightstalkres isn't fun even for well-equipped, high-level Couriers. They're extremely fast and deal serious damage; a group of 4-5 will tear you to shreds in seconds. Stealth doesn't work very well with them after the first shot, silencer or not, because they have very high Perception. The best way of dealing with them is hitting them with Explosives when the pack is tightly grouped, or shooting from high ground which they can't climb. Failing that, automatic weapons with hollow point bullets are your best bet; Nightstalkers have no DT and don't have a lot of health. Your earliest encounter with Nightstalkers may be in the mountains halfway from the Mojave Outpost to Novac, or on the road between Wolfhorn Ranch and Ranger Station Charlie.

If the road isn't safe, tag along with a caravan merchant. At low levels they are better armed than you are, and can handle most threats found along their route. And if they happen to kill someone who is trying to ambush them, they won't mind you looting the body. The stretch between Wolfhorn Ranch and Novac has Nightstalkers, Vipers and Legion troops and as you pass the bridge, two caravans spawn right in front of you. It may be worthwhile to slow down your pace and play a caravan guard for a short while.

This is very sound advice. I do the Bighorner thing on most of my playthroughs, plus I get Bighorner Steaks out of it.

Also, if the Caravan Merchant dies, loot his body. It's what he would've wanted.

Vary your ammunition by target. AP bullets should only be used against armored targets. GRS, DC, & most human enemies are good examples. HP bullets should be used against all unarmored targets, mostly animals. Some interestingly high level enemies suffer serious damage from Hollow Point rounds.

If you see something blue with orange wings, run the hell away. It's not alone, it's just as lethal as a Deathclaw, and is 3 times as fast as you(like a Deathclaw).

If you see bigger, funny colored geckos...well. If they have spikes on their backs & are grey, they're Fire Geckos, and are threats to Lvl 20 Couriers. Draw your own conclusion. If they have yellow-golden skin, they're Golden Geckos, and they mean there's a radioactive zone near.

-Nukeknockout