Skills
Shield Compensation - 2% less cap used for shield boosters
Shield Emissions Systems - 5% reduces cap need
Shield Management - 5% shield hp
Shield Operation - 5% shield recharge rate
Energy Systems Operation - 5% cap recharge rate
Energy Management - 5% cap increase
If you are going with boosters and more active setup, you want to bolster your recharge rates as best you can. Assuming you are caldari, you should get at least lvl 3-4 on all core shield and CPU related skills ASAP. I missed a couple of these for a long time.
Mid-slot Modules
Boosters - the core of active tanking, they repair shields
Boost Amplifiers - 30% boost increase
Extenders - simply increase shield HP
Flux Coils - jack up shield recharge rate with lower shield HP
Power Relays - jacks up shield recharge rate with lower cap (avoid if you can)
Capacitor Rechargers - jack up cap recharge rate
Hardeners - 50% increase in one of the 4 core resist categories, uses cap
Resist Amplifiers - 32.5% passive increase in core resists, doesnt use cap
Low-slot Modules
Reactor Control Units - boost to power grid
Power Diagnostic Systems - boost to shield and cap recharge rates (use these a lot)
I found that when i first started running missions i had to constantly play around with my setup. You want to do research on the NPC you are facing and then get hardeners/amplifiers as needed.
Use the PDS like a whore. They are the ticket to tanking when getting started, in my experience.
Stacking hardeners/amps will cause something like a 50% cut in each of the subsequent modules. So, first hardeners is 50% and the 2nd one will get you like 25% beyond that. You can mix n match the active and passive resist modules, too, to try to get your resists way up.
NPC info:
http://eveinfo.com/npcships/
http://npc.elfarto.com/index.php <-- should work ingame
Ideally, you get a balance where your resists are able to significantly cut down incoming damage while your recharge rates allow you to cut back on the Booster usage. The more you rely on recharge rates instead of total shield HP, the more you need those resists up high.
It's possible to go heavy with shield extenders at the start, while your skills are still low... then just warp up and recharge as needed. In time, you'll find you may be able to literally tank passively... relying on shield recharge and strong resists rather than boosters.
I hope this helps.