Do not try to ADS with the guns, get used to hipfire.
Range combat = short bursts
SMGs are love
SMGs are life
Do not use Tone, she's the FOTM
Try Stim (it heals you too) instead of cloak.
This doesn't apply to every gun. G2A and Hemlock both require ADS, their hip fire is completely inaccurate.
Other tips:
Don't call in your Titan until you see other players on your team with either a Titan Ready (indicated by a grey bar) or a Titan in play (a grey titan icon).
Stay off the ground. If theres a wall near you run on it, jump to another wall. If you do have to hit the ground, slide or double jump and get to another wall asap. Use rooftops, but don't stick to one for long unless you're communicating with your team and they've got your back. Simply running on the ground makes you an easy target.
Make multiple pilot loadouts. I like to keep at least one cloak loadout for it the other team drops a ton of titans at once, because it makes it easier to steal their batteries and deal damage (which speeds up my titan timer).
Do not ignore the AI bots. Shoot them, they will speed up your timer and give your team points in any mode they're in.
As crazy as it sounds, you WILL forget you have grenades. A quick 1-2 of grenade+fire is tough to survive.