Originally Posted by: shan5If my song starts with Am chord and other chords are GM and FM and CM.....what scales can I use , now???

What you need to be doing is looking at which parent scale your chords come from. There are many options open to you in terms of scle choice, depending on the sound you want. You can also choose to improvise using one scale that fits all chords in the progression, or to shift like Jazz players do with the chord changes.

Depending on how fast the changes are, you might find you're only playing a couple of notes from each scale before moving on. You can either work on diatonic theory, or just play around until you find something pleasing to your ear...