In a new game, I normally make a character and he becomes my training guy. Just trying things, learning the skill trees, different skills, etc. I read the forum a lot to pick up some tips - and not all tips are good, btw. But you need to kind of figure out what makes sense.
Then, at about level 10-15, I build a new character, and this is the character I play with the rest of the way.
So, my level 32 assassin/thief is a bow user. His skill is up to 3X damage because of sneak attack. I also take enchanting, so he has an enchant on the bow that hits for 25 stamina. Most NPCs I can one- or two-hit. Also have a helmet that adds 20%, heavy armor gloves adds 25%, and ring that adds 25% more bow damage - so total that's a 70% increase in damage. Now yesterday, I went up against some pretty powerful priest guys on the next to the last quest for the mage guild, and it took a few more hits to kill them. But again, two sneak attacks with 3X damage and one was also a critical hit, so only needed 3 more hits after that - easy.
So, I put perk points in archery since that's my primary weapon. I also carry a 2H enchanted sword in case I have to go toe to toe (last resort type of thing lol) but I don't put perk points in 2H - level as I use it). I sneak everywhere. One thing about sneak, if there's no NPC or animal around that can detect you, your sneak skill will Not increase. You can almost bet that any old fort you find is full of enemies - so sneak approach, bow, 1-2 hits and dead. Inside dungeons, sneak all the time (except if the dungeon is empty). It levels quickly.
I put a few points in light armor and enchanting. The first few points in light armor will increase your armor level and really help. Level enchanting slow and careful. Lock picking and speech I don't put points in, that can also level itself.
I also play a level 21 pure mage, so I switch characters every other day. Do different quests/guild quests. But, you can learn from each other. The mage wears light armor that I enchant.
Hope this helps a little.
Good luck.
PS: I play slowly, so sneaking around etc., fits my play style. If you're one of those players that does everything quickly, a lot of what I wrote won't help you.