Now that you can get free Pulse Cannon's it's made the use of Reserve Powercell + Pulse Cannon a lot harder or totally pointless. If you still want to use it, make sure the buff for the free Pulse Cannon isn't on your bar otherwise it's a complete waste.
Hold the Line is extremely useful for nullifying plants, like when Sunder throws the knife at you and plants you to the ground. I use Tenacity the first time, then Hold the Line the second time and then the last time, if both are still on cooldown, I'll drop Riot Gas on the third one and hold out till I can move again. I also use Hold the Line every time I'm just about to get out from behind a rock on the Titan IV fight so I can get back to the boss asap. Some may want to use it if they're the one who ends up targeted with the grenade, but I find I can get away from the rest of the group easily enough anyway.
Speaking of Riot Gas, I'm sure it makes no difference and it's just my brain at work, but even though the tooltip says it affects the enemy units and not the player or other players, I like to stand in it... makes me feel safe *looks around* lol, just wanted to say that. XD
Um... what else. Adrenaline Rush, now that it activates at 30% health, you can freely just hit it as a precaution any time your health gets halfway or just below and you think you may be in trouble and it'll activate automatically, even much later on, if you do end up going 30% health.
Of course, this makes Reactive Shield a much more rare move to use. I only ever use it for extreme emergencies now since it's the only real defensive cooldown we have. It's too valuable to waste on anything but the most life threatening situations and you can't afford it to be on cooldown when you need it. Riot Gas and Energy Blast are the ones you always use as soon as they're useable.
Shoulder Cannon is really useful while stunned since it's still usable. I start firing the hell out of it when I get planted into the ground by the Titan VI in S&V and can't get out of it. It's also good to use if your health is low and the healers can't get to you. Fire off all the rounds and get back 20% of your total health. I'm guessing this is the replacement for what Adrenaline Rush use to be. I don't really use Shoulder Cannon for building threat since I already have a lot of other abilities that can serve that function well. Shoulder Cannon is only useful for stunned situations, quick heals and low ammo situations to maintain threat.
I'm sure there's more but I can't really think of it right now... most of this is muscle memory at this stage.
Oh yeah, defense, defense, defense... stack up that defense. I've been using the guide in this thread to guide me on what balance I need: http://www.swtor.com/community/showthread.php?t=616779
Also, in the Operator IX fight on TFB, can't use High Impact Bolt on the first phase with the coloured orb things flying around since it activates the Ion Cell AOE which ends up damaging the orbs.