Here's a quick tutorial on how I level feet on a table, chair, cabinet etc. I am using a cabinet as an example.
Despite your best efforts, when the legs are finally in place they are often not sitting flat on the floor, or the cabinet is not level. This is especially the case if the legs are curved.
1. Use shims or wedges to level the case. I was lucky in that I only needed two identical shims to level the cabinet. Sometimes each leg can need a shim of a different thickness. (Make sure the floor itself is level and flat obviously first!)
2. Hammer a nail into a block, saw the head off and file it to a point. Try to make the point of the nail level with the bottom of the shortest face of the shortest leg.
3. Scribe a line round each face of each leg.
4. Put the cabinet on its back and saw the leg ends off at the scribe line.