Practice right after your lesson, but not right before.
You had a great lesson and covered a lot of new material. The next day you begin your practice and.....you can't quite remember what the teacher said about a rhythm or fingering......has this happened to you?
You'll find that if you review what was covered in your lesson right after your lesson, rather than waiting until the next day, you'll remember more of the details discussed. Shortly after your lesson, before you get involved in another activity, take your music out and review what your teacher addressed. Five minutes may be enough! Was there a particular rhythm you were working on? A special fingering, dynamic or phrasing? A quick review right after your lesson will help you to retain the new information and keep it fresh in your mind for your next practice session.
Your lesson is tomorrow and you realize that you haven't done enough practicing during the week. You get your clarinet out and practice a full hour right before your lesson......now you are in your lesson, things are going well.....and suddenly your embouchure dies....you can't play another note! Has this happened to you?
It's best not to practice right before your lesson. If you do, you risk tiring your embouchure and not having enough endurance for your lesson. Cramming for a lesson doesn't work anyway. You will progress best by keeping to a regular, daily practice schedule.