Alternate Picking, No Excuses
How to play
Choose a simple scale or pattern, such as one octave of A minor pentatonic or a major scale on two strings.
Pick every note strictly down, up, down, up with no exceptions. When the pattern changes strings, the picking direction does not change.
Start slowly with a metronome, or watch your picking hand to check it stays in motion.
Challenge
Play the pattern ascending, then descending, then starting on an up-stroke. The up-stroke start is harder than it sounds.
Tips
Keep the picking motion small and relaxed, and let your hand move from the wrist.