Prep: dry, bare, degreased
Take off any old polish and let your nails sit for a minute — freshly stripped nails are damp with solvent even when they look dry, and lacquer laid on solvent lifts in a day.
Push your cuticles back gently with a towel after a shower, or with the flat of your thumbnail. You are not trimming anything. You are just making sure the lacquer meets the nail plate rather than a fold of skin, because skin moves and lacquer doesn't, and that edge is where a chip starts.
Shape the free edge with a file if it's ragged, moving in one direction rather than sawing back and forth.
Then degrease. Wipe every nail with a prep wipe or a little surgical spirit and don't touch them afterwards — not to check they're dry, not to move your hair. Your fingertips carry oil. That's the whole point of the step.
If you moisturise your hands first, you've undone this. Hand cream after, always.