MTG Salvation

I second the pre-con suggestion. However, if your group out-grows the pre-cons and want to build something from scratch, I think commanders with a very clear build-path are a good start. Creature tribal commanders would often fall in this category, as would, for example, omnath, locus of rage. Such cards he;lp in that they put further constraints on the cards you could be using by making it clear what they need to win. Creature tribal commanders want their tribe to be represented, while omnath wants you to play a whole bunch of ramp to enable him, for example.