When you are expressing yourself in a guitar solo, the major scale is a great place to start but don't make the mistake of always playing the scale from top down and back up, that will sound like (do,ray, me, fa, so, la, ti, do, etc..) and will get redundant real quick.
Starting a solo on the root of the key you are in (while in a major scale shape) is usually where beginning soloist start and there is nothing wrong with that. If the key changes in the song, you can sometimes stay in the key you are already soloing in while creating a different sound for your solo, this is called a guitar mode, or "modes of the guitar". There are all kinds of modal sounds you can create, Frigion, Lidion, etc. and all depend on what key you are in and how many steps you are from the key being played in the song. Look up "Guitar modes" on the net and you will get all kinds of info.
Another thing, if you are going to play the major scale to start soloing, learn to play arpeggios shapes to help break up your major sound.
Hope that helps.