I noticed my cornering confidence improves as my ride progresses (which seems be a little odd). Is there some sort of cornering warm up routine I can perform before a ride to help be confident throughout?
There's a common enough drill that we teach kids on our HS MTB team that could also serve as a warmup. The idea is to practice keeping the body vertical (and off the seat, of course) while turning the bike into the turn. The foot on the outside of the turn is kept down. A variation (an "I trust my bike" exercise) is to maintain that posture while keeping the bike moving straight-- essentially riding straight on the side of the tires. The first exercise is more useful, imho. We've seen an improvement in confidence as the kids understand a bit of the physics of the turn and see that there's more to it than, "fling yourself into the corners and hope the brakes are good enough".