I usually quit at 80# and then put on a couple slightly diluted (mineral spirits) coats(no sanding). After those first 2, sometimes 3 coats are bone dry, I'll flat sand(block) with 100-120#. Those first coats seal the wood and give a rough foundation that you can be sanded flat. There's not a lot of sanding to do if you do it this way. Recoat - allow to fully dry - flat sand with 120-150#. Next time go to 180-220#. Do that a couple times and your work(or lack of...) will show great results. You can do your last coat(s) with even finer paper or a 3M fine mesh.