-Assault Scope + Weapon Pro actually seem pretty powerful on PC because the recoil increase hardly makes a difference. You give up some close-range power in favor of some long range power. I love this on Feline and Grendel the most.
-Nano vision can see through walls and ceiling. Make sure no one is sneaking around you. Should always use it when entering a small space to be sure no one is camping there.
-Stealth enhance + mobility enhance for someone who likes the safety of being stealthed but still wants to sprint around.
-Nano recharge is probably better for you unless you're getting a ton of kills using energy enhance.
-Hit "Q" to turn on armor mode before you start shooting. No need to waste all your energy shooting while stealthed-- even if the kill is a sure thing.
-Silencer causes your damage fall-off to occur at closer ranges for Feline and Grendel. Opting not to use it makes them both better at longer ranges.
-2 hits to get a melee kill if you're in armor mode. 3 hits if not. Doing just about any damage with a gun and then meleeing with armor mode should get a kill.
-Without silencer Grendel = 2 good body shots for a kill. Very useful on maps like Skyline where you can get to the roof and unleash. I recommend Assault Scope + weapon pro in combination with it.
-Sometimes your energy will start to recharge in the middle of a fight-- be sure to put armor mode back on!
-Dont re-stealth INSTANTLY after killing someone. At this point in time, it is likely someone else will start attacking you and you will die instantly. Wait a second and try and find whoever is de-stealthing to shoot at you. After a moment, stealth and sprint to safety.
-When to use the Gauss rifle? In team game modes. Its high damage means that if an ally or grenade has so much as nicked them, they will die in one hit. It can also take down gunships in only a few shots due to its massive damage.
-Kill-streaks activate energy recharge, making energy recharge and retriever a good combination if you can maintain decent gunship uptime.
-Place nano-suit jammers on points in Crash Site. On certain maps, there is an obvious part of the map you want to control, such as the roof in Skyline or the most elevated section in "Downed Bird". Place nano-suit jammers here. Having a single class with Armor Enhance III means you can still assault and take a point when an enemy has carried out this strategy.
-Maybe I'm a fool for not realizing this until someone pointed it out in the comments: you can shoot at and destroy nano-suit jammers.
-Single-shot jackal is a one-hit kill at close range and a two-hit kill at medium-ish range. Very powerful on certain maps and game modes.
-AY96 is probably the best sidearm for players who don't quite feel comfortable with the handguns. Don't force yourself to use a handgun if its giving you bad results.
-Having trouble seeing other players? Don't underestimate "Visor Enhance" for your normal classes. It is more helpful than it might seem.
-Don't let your team get torn up by gunships. Have a class with the JAW equipped.
Will add more.