Okie, more info is good. My advanced apologies if i offer something so basic it comes off as insulting, but just trying to be helpful.
To flourish in an STF, you absolutely must have the following skills:
Tactical Team 1: for the shield redistribution and clearing out borg boarding parties. Level 1 is just fine
Hazard Emitters 2 or 3: its a great hull heal for yourself or teammates, and puts out plasma-torpedo-fires that you'll eat lots of (and can really kill you on elite; they're not always just a mild itch)
Additionally, I find these quite useful but not exactly MUST HAVE
Transfer Shield Strength 2 or 3: Good for both yourself, or if you realize a Cube is really angry at a friendly escort you can help that guy out. For 3, find it on a BOFF on the Exchange then train your own BOFF in it.
Gravity Well 1 or 3: In all 3 space missions, one of the objectives requires you to keep Borg ships from getting to a certain place, so being able to simply shut down a whole group of them for 12-20 seconds can be a mission saver if used right. Also good to use on Cubes for some extra damage and to cripple their high-yield torpedo fire.
Tractor Beam 1: For the same reasons you would use Gravity Well, Tractor Beam is a backup you can use on 'the one that got away,' or to hold ships near each other when one is exploding (which I use a lot in Cure Space), and it only costs you an ensign slot (if you have one to spare, depending on how you use your universal). Can also drain slightly shields when using the correct DOFF.
Polarize Hull 1 or 2: Borg love to tractor you, then hit you with high-yield plasma torps or their hull cutting beam. If they lock on, its either break free or get ready to tank, and on a sci ship breaking free is easier.
As for weapons, a pair of dual beam banks and a torpedo fore, 3 turrets aft, will give you decent damage to your front arc and still let you use subsystem targeting.
If you want more detailed instructions, there is also
Cygone's Nebula Build which maps out exact boff skills, captain skills, consoles, everything, to turn a Nebula into a monster gunship (dependant on pilot of course). Its not much for healing/debuffing though, so depends on how you like to play.