maybe one day You could try some simple guitar tab lessons
if You do, check out this place:
http://www.wholenote.com/default.asp?src=l&l=6102
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The guy who mentioned trying to play the solos of good guitarists, that was good advice. I don't know if You have the means to get any of the hardware, but there are machines out there now that are around $100 each, which take CD recordings and slow them down, without changing the pitch of the songs. If You could slow solos by other artists down, one thing You'd find is that almost every solo is just a "riff," like You're already good at, just sped up.
One way You could make Your own original solos is to just play the riffs You're used to playing, pick one main note from them, and play that new riff faster and faster and faster. Practice different picking techniques (I'm sure there are more guitarists here who could go on and on all day about how to do sweeps and other great solo picking techniques) with the same riff. Practicing what You already know and just speeding it up goes a long way to starting to solo. Practice all kinds of funky rhythms or suddenly ripping into a powerful set of notes then stopping and jumping somewhere else on the board and starting up the ripping again. Do this practicing slowly at first, imagining how it would sound if it was going really fast. Then just speed the same thing up more and more. One way to practice that is to record something, at slow speed and listen to it a lot, so You remember any cool riffs or runs You came up with. The more You practice speeding it up gradually, the more You'll develop the skill to play an actual riff or melody really fast.
As for sound, without knowing Your setup, I can only say, good equipment gives good sound. A master guitarist can slam a wrench onto a fretboard of the cheapest guitar and make it sound like a great solo, but, that's a master guitarist. The less skilled a guitarist is at playing, the more they're gonna need good equipment to get a good sound. Maybe You could list Your rig and instruments and we could figure out how to adjust things to get a better tone. Part of the sound, of course, is how well the guitarist is singling out just one string and how the guitarist's fingers press the strings/frets and how the strings are picked or muted. Still, if You know how to adjust the tone settings or equalization on Your amps and guitars, You can hide a lot of problems with playing until You get better. Also, there are a LOT of effects on the market these days that clean up and change a sound.
One thing You might try, for solo practice, is this example. Hang out around the fifth and eighth frets right across the board. Practice JUST using the open string, the fifth, sixth, seventh and eighth frets to play with. Learn how if You play a fifth fret on some strings, it's the same as the open string on another and eventually You'll find some cool rhythms You can do very quickly by switching between the open strings playing while You run up and down the 5th, 6th, 7th and 8th frets. What You learn while doing this can be transferred up and down the board pretty much, eventually switching so You just use the 12th, 13th, 14th and 15th frets.
As You figure out what You like to play in solos, when You're jamming along, Your mind will sometimes automatically go back to the fret playing You'd been practicing. I mean, You might be soloing on the G string and suddenly, when Your fingers are near the 5th through 8th frets, You just rip into a run back and forth across the strings, jamming quickly over those frets. Then You go back to the G string or whatever.
Sounds like one of the first things You need to do is figure out why You're getting such bad sounds from those other strings, whether it's the equipment or Your fingerings.