If, like me, your pop-up isn't the best (since getting back into surfing and having been surfing the grand total of two times in the past month, I clumsily and slowly lunge to my feet, often wiping out) there are some videos on YouTube which show how to do pop-ups. Watching these and doing land practice if you can't get into the water as much as you'd like will help a lot. I am watching loads of surfing videos, not kids ripping it up on shortboards - yes it looks good but my shortboard days are long past now and, even then, I didn't exactly rip it up - just Joe and Jane Average Surfer, and my land-based practice (pop-ups) is getting better and better.
Here are some of the pop-up vids. This Holly Beck one is, I think the best.
This one, from the Online Surf School, has three methods. When you go to a surf school, they don't advise using your knees (or a lot of them do) and using your knees can be a bad habit to break. The 'Aussie sprint' pop up is interesting, I've not seen that one before and, I think if I tried it, I'd wipe out more than actually get to my feet (even more than I already do). But, whatever works.
Ben's Surf Clinic shows, again, a method of using your knees. That's always something I tried to avoid but, again, if it works for you it works.