One thing I would advise it to decide what sorts of music you imagine you will be playing, and look for lessons geared toward that kind of music.
Example: There are ridiculously difficult exercise books that beat fingering and classical technique into your skull with a sledge hammer, and that's great if you are planning on playing Rachmaninoff or Chopin, but if you are more looking for the ability to play chords and simple 'pop' note sequences, then you don't need that kind of training approach.
There is also a distinction between music theory and piano playing instruction - bottom line is to find something that will teach you so that you can play the kind of music that is motivating you to learn in the first place. :)
Bob Bone