Quads and other leg muscles still sore after 3 days (from first workout), what is the best way to get rid of lactic acid build up?

Overdoing workouts: It sounds like you did too much during your first workout. Enthusiasm is great, but you need to go slowly to start. Get some guidance from a trainer as to how to get a workout routine started, make sure you are adequately hydrated and do warm up and cool down stretching . These things should go a long way to prevent your post-workout soreness.