Many people dont understand the real theory behind the music they play. To come up with some cool solo's just get hold of a copy of some basic scales e.g 'A minor pentatonic' then attempt to create a solo using the notes within that scale. With the riffs, its purely just looking how other metal riffs are created followed by practise. Try and get hold of some good tab and try and pick it up from there. For soloing, try getting hold of a guitar mag, they will usualy tab some famous songs (jimy page stuf etc) then u can see how a solo is created.
Keep it real man!

(Anyone else feel free to tell me im talking c*?p, or further enlighten this person)