Captain -- please let us know what faction you are playing. Romulans/Remans can play both ways.
Federation side: Human Leadership is a plus. Healer, look for a Betazoid Science officer (note: Males go for $1000 credits, females $50K credits) with telepathic trait (on ground - Reduced threat, Increased Team Regeneration) and +10 perception. Saurians were mention above with the "efficient trait." I have a few as engineers and they are good ground fighters. Often overlooked, are the Bajorians (I use as Science officer) for their -- "+0.2% Healing to Shields and Hitpoints (Engineer)" or "10% bonus to healing abilities used on you" (Science) I think the trait is called "Spiritualism." Source: STO Memory-Alpha
KDF side: More at home here. Just for regular play, I have four wonderful Orion females on my ground team; 1 Tac, 1 Sci (healer), 2 Eng (turrets/shield gen). They are not wearing KDF battle armor. For more serious ground adventure, I use my Jem'hadar Tac Boff (game reward) with full Jem'hadar set. Lethean Engineer with Superior Mental Discipline and Rapture (also has Efficient, but that is a space trait), Android Science for healing and self-rez, and Orion Female Engineer with Superior Seduce.
Romulan KDF Officers has the best of both worlds.
There is no secret, but it comes down to "trait" hunting and what you want your team to do. "Superior Operative" on a Romulan will cost you. This will help:
http://sto.gamepedia.com/Trait
Through the Rep system I was able to pick some excellent MK XII purple equipment for the troops. I also keep a few extra rifles in my inventory to swap out depending on the foe (undine/voth/tholian). I also have a secondary team equipped for melee for use against Borg (no re-modulation to worry about) . Give you absolute best shields/armor to your healer and a long range weapon like the Borg Arm.
There is also a variety of forum post on various blogs about ground teams on STO, especially over at Star Trek Academy. Good hunting.
Cheers