Guitar solos revolve around the improvisation of scales. Hence, knowing the scales very well will help you in learning guitar solo. I feel that the major, minor, harmonic and pentatonic scales are the most useful. Not only does it increase your overall movement, it also makes sure you use the correct fingering. Of course another important way to master guitar solos is to practice. The more you practice, the better you get, it is the law of nature.

Soloing is more than just a couple of scales, and patterns. It is used to express feelings. The pentatonic scales give a rather sad feeling. So, if one is looking to make a sad solo, he or she can improvise on one of the pentatonic scales.

I am going to give you an example, the Harmonic Minor Scale and the pentatonic minor; both are awesome and unique scales. Gary Moore used the Harmonic minor scale for blues sound, in the song 'I still got the Blues'. Hopefully, you can clearly see that solo are improvisation of scales.

If you don't improve your soloing with a bend, a pull-off, etc. Your solo may still sound like a scale. So what can you do in order to play a good solo? First of all, you must know the key of the song. Mostly the key of a song is the first note you start playing on it. Always make use of techniques like bending, tapping and such to add colors to your solo. Take a look at dragon force 'inside the winter storm' or practically and dragon force songs, played by Herman Li, you will realize that his solo is filled with different techniques such as power chords, sliding, tapping and palm muting.

So, the bottom line is, master your scales before learning any guitar solo. Then, try to improve the solo using various types of guitar techniques.