IMHO, the best place to start is the major scale.
I'm a fan of the CAGED system, not everyone is. If you're receptive to that, you might start by learning the major scale in each of the 5 shapes.
Another approach which is not strictly CAGED but will get you similar results, learn the major scale starting with the root note on the 6th string, then learn it with the root on the 5th, then the 4th.
