If it's just you and your drummer, you'd be somewhat limited on busting out a typical solo that can stand on it's own without a bass or another rhythm guitar. But I'd say the most basic approach is to play a chord/riff progression, 12 bar blues for example, and add little fills (melodic lines, trills, pull-offs, etc) in between chord changes or for fairly brief passages and build from there. Otherwise, unless it's a pre-written solo, it's much more difficult to improv lead guitar without backing and keep the flow of a song.