Play a melody note write the notes down in order of pitch and number them then shift the notes so that the numbers refer to other notes but the rough relationship between the notes is similar and then work out the melody in this new alternative.
This is a very robotic means of using a process called modal transposition. If you have the fretboard or ear to do it some other way then do so but it might help you get used to the process until you can do it properly!
Lots of neo-classical shredding uses modal transposition. don't use it in excess, it gets samey and dull. Do unexpected things. Bear in mind that what can sound like a mistake to start with can then be made to sound right by choosing later notes carefully.
Mix up fast and slow passages. Pure shred is dull and lacks expression - you can't bend,vibrato, violin or pinch humongous shreds after all. Slow stuff doesn't always impress shred-heads who like the melodies to really tax their abillity to comprehend the passages which speed does. Mix em both and hey.. woooohh!