As of 2.5
See here for an EXCELLENT Dulfy guide on Shield Specialist Vanguard (Tank). Read it thoroughly to fully understand how great you can be tanking on a Vanguard.
Most importantly, please review how Taunt works. This is imperative for learning properly how to hold aggro. I'll be making a post in the general section specifically on how Dps and Tanks work together around the Tank's Taunt mechanic.
http://dulfy.net/2014/01/05/swtor-shield-specialist-vanguard-tanking-class-guide/
Has recommended stats/gearing, recommended rotations, explanations of skills, etc.