Here is a practice track in a folk rock style, based on the chords to “Knockin’ on Heaven’s Door”, a perennial guitar favorite – mainly because the chords are very easy:
||:G | D |C | |G |D |Am |Am : ||
To solo over these chords the best place to start is in the key of G major, as all the chords contain only notes from that key. So get the G major scale under your fingers, and make use of the following track to hone your improvising skills!