This is what I do if I want to feel sore:
After the last set I plan on doing for that exercise, go down 5 or 10 pounds and do that till failure (maybe 2-3 reps). Then go down 5 or 10 pounds and repeat. I went down to 10 lbs doing dumbbell curls. I'm sure I looked ridiculous but it sure felt good
I'll do that maybe once or twice a week.
But then again, I'm in the process of restructuring my workouts so I dunno if I'll keep that up. Good luck in your workouts!