If you practice with a drone, you'll also train yourself to hear when you're out of tune.
If you're playing scales and arpeggios, doing this while using an electronic keyboard to provide a relevant chord is very helpful. (My Yamaha keyboard allows you to start a rhythm pattern which I use as if it were a metronome; then if you key in a chord with your left hand, you get the thing playing along with the chord you keyed in, plus at the indicated rhythm and tempo. So if I'm practicing C maj/A nat min, I'll key in an A minor chord, and so on.) If your keyboard doesn't have this capability, you just tape down the notes A, C, E and there you have your A minor chord drone for as long as you can stand it.