The notes that sound the best are the notes in the key. In A minor that would be the notes A B C D E F G. You can add an E Flat to the scale to make it a blues scale if you like. When there is only one chord playing in the backing track it's called a Vamp. A Vamp is useful to get use to whatever key your getting familiar with or practicing. Any combination of these notes sound good. The thing to learn is a lick that fits over the vamp. There are 3 arpeggios that work well with that chord. They are Aminor = ACEG E minor = EGBD and B minor = BDFA

You can play from any note of the scale. Ex. From D - DEFGABC
From E - EFGABCD. If you play every other note from any note in the scale you have the arpeggio. Ex. A b C d E f G = ACEG