There is a certain grain in the wood - one can not sand past this point.
I use 180, 240 and 400 for the finish. 180 for the first sanding, 240 for the fine and 400 only for fine details. Oh, and also some very fine steel fleece after the finishing.
Put some tape on the back of the sand paper, it will last much better and is easier to work with. Otherwise one has those ripped, scrambled bits of sand paper that harm more than sand the piece.