Hi John,
The fact that you have been playing for so long will benfit you a lot in the transition to lead. First things first, learn some basic scale shapes and patterns. Pick a key eg A and work out the scales across the fretboard for major, minor, harmonic minor and pentatonics - this is as good a place as any to start. It's boring as hell learning scales but you will find that you probably know a lot more about the fretboard than you think when you start practicing. Assuming you can do alternate picking, the next step is to practice established runs, 123's ascending and decending, 1234's ascending and descending in the various patterns available throughout each of the scales. Then start trying to create your own runs.
The best way to create a piece of lead in my experience is to listen to the backing music then either hear the lead in your mind or hum along some improv. Then sit down and work it out. Eventually you will be able to directly play what you want to straight onto the fretboard - it just takes a lot of practice learning the fretboard before you can play an idea directly without having to work it out first. I'm not sure what level you are at yet so some of this could be to advanced or too basic. I'm self taught too and that's what got me going. Hope some of it helps.
What kind of music do you play or want to play anyway? That will have a bif bearing on how and what you practice.