here's something you can do. Figure out what key the song is in. Typically, its the last chord in the progression or the last chord of the song. It holds true for a lot of rock songs and will work mostly work for easier stuff that isn't overly complex. Next, learn the blues scale and play that scale corresponding to the key signature. The blues scale kicks ash because its a pattern that you can just shift up and down the fret board. So if it ends in the C chord, then find the C on the low E string and that will be the root for your solo. I do this when I improv ZZ Top and other rock based songs and it usually works pretty well once you've gotten used to the notes/patterns.
Here, read and practice this.
Solo Guitar - The Blues Scales - 12bar Blues Guitar
Go up and down the scale until you know that pattern then just play with it and you'll develop your skill as you go. Oh, and the difference between the major and minor scales are shown as the note in BLUE. This is the blue note which is a good way to put some feeling into that baby.