Many polish manufacturers suggest using a damp cotton cloth to apply polish to the boat hull, as particularly in hot weather this will enable easier application.
Use a microfibre cloth to polish up as this is much quicker than ordinary cloths and removes any residue rather than smearing it.

Avoid hot and sunny conditions when applying the wax but if this is unavoidable work small areas once at a time and ensure that the surface is polished up before it becomes baked on. If the wax proves difficult to remove go over the surface again with more wax, applied with a damp cloth.

(Thanks to Farécla for the tips)