Great question, Bee! The best thing to do before applying anything to the lip is to use a Lip Primer. If you find that the natural creases in your lips are really deep, I recommend using a Lip Conditioner first (before the Lip Primer).
Lip Conditioners are great for helping to stimulate the collagen in your lips and "fill in" the creases. My new favorite lip conditioner is from Avon and it's called Beyond Color Plumping Lip Conditioner SPF 15 with Double the Retinol and it is AMAZING!! I use the conditioner all throughout the day b/c it makes my lips feel so good and smooth.
How To Apply: Apply all over the lip like you would a lipstick and blend in with your finger or a lip brush. Allow to set for a minute or two, then apply Lip Primer.
For Lip Primer, I use MAC's Prep + Prime Lip. It doesn't advertise to have a plumping agent in it, but I do notice that my lips become more full and supple when I use it.
How To Apply: Apply all over the lip going just outside/above the lip line (don't worry it's clear so you won't see it on any skin tone!). Allow to set for a minute or two then apply liner, lipstick and/or gloss as usual.
I hope these tips help! Keep your questions coming and definitely let me know how you do with these tips.