What can I do to decrease swelling in my lower lip caused by puncturing a mucocele last evening?

Time. It will take time to heal. You could try some ice. If it is not better in a couple weeks see an oral surgeon.
Ice. If it's not infected you could put ice on it. If it is infected you would need to see a doctor for an antibiotic prescription. Mucoceles have a tendency to recur.
See a dentist. Puncturing a mucocele can decrease the size of the swelling temporarily, but the swelling usually returns. The recommended definitive treatment to eliminate the problem is to have the mucocele removed. Your dentist, oral surgeon or ENT can perform the procedure for you in the office with local anesthesia.