I leveled my Guardian to 50 as a tank (then switched to DPS), so I can talk about the trip from level 30 until 50 or 55. You know when you complete quests and you get the option of getting planetary commendations? Pick them over the crappy green gear. You can buy orange heavy armour and fill it up with armourings, mods, and enhancements which you buy either on fleet (Supplies section outer ring) or on the planets themselves.
Anywho, I don't think you have access to any real tank gear (which gives absorb/defense/shield/accuracy) until level 40-ish. (Maybe you can start buying stuff that gives at 30? It's been a little while.) As a result, what I did was always picked the mods which gave high endurance. (E.g. pick Guardian armourings over Might armourings.) Whenever I did flashpoints, I would be miles ahead of everyone else because I had so much endurance. Because I wasn't sacrificing any real tanking stats, healers didn't have a tough time healing me. Once you have access to stuff that gives defense/absorb/shield, please pick that over endurance though.
As for Vette, pick gear that is high cunning. (E.g. Skill armouring over Patron armouring.) Again, modifiable gear will give the best stats.