| Think of scales and melodies as you would of chords and songs. Chords are used as the harmonic building blocks of songs... string chords together in a tasteful way and you have a song. Same goes for scales: they are the building blocks of melodies/solos. So if you tastefully string together notes of a scale or scales, you'll have melodies or lead lines.
It's a good idea to approach using scales from a couple of angles. First, try to transcribe (or get sheet music/tab for) songs you're into. Perhaps you're a fan of a particular guitar player and like one of his/her solos; you should learn as many songs and solos as possible. From there, try to figure out what fingerings and scales are being used in particular solos. You claim to know the fingerings well already, so once you begin learning your favorite lead lines you should begin to quickly recognize parts of fingerings in use. Also, keeping in mind that same notes can be played in several places on a guitar, you should experiment with playing the lead lines in different fingerings. For example, if a given solo plays an E on the 2nd fret of the D string, locate that same E at the 7th fret of the A string and find the other notes of the solo in that position, etc.
Other than transcribing, you should experiment by putting your own solos together. Again, you could use your favorite song(s). Figure out the key and scales used and create. You could begin by using previously learned solos, and then create something new from there.
The scales that are most useful and that you should know well are the Pentatonic (minor and major) and 7-tone Major (and it's derivatives) scales. | 
Linear Mode
