I equip, I think it's, the HCOG Ranger on almost every gun except the ones that don't have it because of that, the zoom of the entire playfield is much more useful for going after people far away than just a zoomed spot in the center with the rest of your view compromised. As long as you can get the ironsight onto the dude the range is irrelevant.
I even do this on the sniper rifles that aren't the Kraber.
KEEP MOVING! AND GO DIAGONALLY! I know I spam it a lot but it really is the most helpful single tip in the game possibly, you really can move in every direction, so do it, and suddenly stop and go in other directions. Make loops on the maps going different directions. Use your abilities, especially the grapple if you're a fanatic for it like me, to be constantly changing your speed and location.
You can ignore when you get killed. After you watch enough killcams you'll realize that lucky shots happen constantly and the main thing you can control is your situational awareness and how you can affect others in the same way.
Sometimes a "feel" for the gun (or titan weapon) can be better than what it does statistically. It's because you aren't even thinking about it, it's just another extension of you.
DON'T FEAR TITANS! One "tip" I would apply though is equip Titan Hunter and get out the Thunderbolt and fire it in the direction of titans then run to cover and repeat, combined you can speed up your titan drops pretty quickly. Combined with auto-eject early on you'll get more chances to test out your titans without needing to worry about dying. (Yes, it "hurts" your team in Attrition but don't worry about that yet.) Once you're comfortable and no longer even afraid of titans you can easily play with the other loadouts.
KNOWING THE MAPS! This combines with the movements, as you learn them you can go places nobody else will go, you can take routes to escape and come back into the fight from new angles while everyone else is fighting in the main areas, etc. You can play the maps solo to futz around in and practice your movement if you want, but really you can just play matches and do this. The other night on Rise I spent most of the match running around on top of the map like an idiot firing down onto people because the match was so lopsided in our favor. I tried to see how long I could keep my wall runs going, etc. Even when I killed people they seemed to not even realize I was doing this for like five minutes straight. Because why? That's right. NOBODY LOOKS UP!
ABILITY! GRAPPLE! You start with the grapple and it's really ideal because it motivates you to start moving and get up high, some of the other kits are best for the "ground" level more often imo. I love the grapple so I'm biased and have stuck with it after toying with the others but it has full physics that you'd expect, you can fire it straight to pull yourself then hop into a fling, you can shoot it at an angle to halt your momentum then pull you in another direction, you can use it to speed yourself up then release to a sudden stop, etc. Do the other abilities have cool qualities? Yeah, but I still love the grapple. The grapple can grab people and titans both. Great way to get to yours as well.
Oh, and cloak only cloaks you to titans, pilots can still see you. I have totally been abusing noobs thinking they're cloaked this week.
Auto titan sucks, don't use it unless you HAVE TO (like to capture points or something), standing there like an idiot firing your weapon is better than auto-titan because you fire faster and more accurately and can use your abilities. Enhanced auto titan is not worth it, any quality PILOT, can take one down simply by getting above it.
AGH! I'M BEING RODEO'D! If you've got a smoke, pop it and CROUCH the titan. It will kill the dude before he grabs your battery. Another tip if you have no smoke, when they grab the battery, they jump off behind you in the same way always as there's only one animation set. With the quicker titans you can spin and melee them as payment. (Back towards a wall so they can't escape!)
KILL THE GRUNTS AND SPECTRES! It builds up your titan meter and helps your team win! But generally once you get in your titan, try to leave them alone if it's not Bounty Hunt. That way your teammates can kill them and build up their meters. (If your teammates are jerks and just deathmatch feel free to get the free points by killing the grunts and such while in your titan as you hunt the map.)
You can roughly aim where your titan drops. A titan drop will destroy another titan. The titan drop and shield will kill pilots and grunts and so on. Feel free to combine this information depending on the match type.
HAPPY HOUR! During this you get five free XP to level up faster. The default happy hour for The Advocate (ADV) is like 3AM eastern or something. The YUM! Brands group's happy hour is midnight eastern time BUT I will adjust it for anyone who'd like to have it set at a different time so they can do happy hours easier to level up. Feel free to join, it won't change anything but your happy hour time and your clan tag!
V is pilot melee by default. I say this because I've seen someone ask this almost every night so far.