You know the drill: You get that little 'your squadmate is down' alert and race towards the first aid icon. Wait! First check they weren't killed by a turret. (Look at the info feed in the bottom right to see what did the damage.) Otherwise you risk a creating a Charge of The Light Brigade-style shambles, as you all get mown down in a couple of seconds. Whenever you're rescuing a downed buddie, first assess the situation and clear out any lingering enemies. Ultimately, even with the clock ticking it's better to use caution rather than risk a domino effect of deaths that costs the whole team the game.
Unlocking the cooler weapons and character types means buying the better equipment packs - 'Veteran' and 'Spectre' - which give you a greater chance of finding a rare item. (Note that the Resurgence Pack adds Asari Justicar Adepts, Geth Infiltrators and Engineers, Batarian Soldiers and Sentinels, and Krogan Battlemaster Vanguards - plus three new guns, the Striker Assault Rifle, Kishock Harpoon Gun and Geth Plasma SMG.) However, don't dismiss the cheapo 'Recruit' packs entirely. They're handy for topping up your stockpile of Cobra missiles, Medi-Gel and Spec Ops items, plus will often improve your standard weapons, which at the higher levels become reasonably serviceable.
The Store also runs weekly promotions, during which 'Premium' and 'Jumbo' packs will be available - so keep an eye out for these. PC and Xbox 360 players should also be sure to play during the weekend events which Bioware hosts, such as Operation Raptor and Operation Beachead.
Participants get bonus XP, and if the operation conditions are met, potentially also some rare gear as a reward. To be eligible you need to have 'upload gameplay feedback' switched to 'on' in your online options. Happy hunting!