Start by learning solos from bands you like. You can then start dissecting the solos by figuring out what sort of scales, chords, arpeggios, etc they use. From there try using the scales etc in your own new and unique ways to come up with your lead parts.

the best way i have found to play leads is no joke mostly just start playing notes find ones that sound good and build from there. one way to find good notes is to use a pentatonic scale hands down the easiest scale to play and learn it goes like this.

lets say you are playing key of A so start on the 5th fret o the low E string from there you would play 5-7-9 then move one string up to the A string and play 7-9 then move one more string up to the D string and play 7-9-11. really really easy to play and throw in where ever. if you need to change the key just make your starting note the root note and your good to go. I.E. if you want to play in E start on the 7th fret on the A string. same pattern as before just different key.