Apply a base, either a specific base wax or a hard wax [green or blue], lightly ironing it in.  When cool lightly and evenly crayon on the wax of the day then smooth out quickly by rubbing with a cork [synthetic or natural]. 

It should be virtually invisible when you've finished.  Repeat the process if you're going on a longer ski.  Several light layers are better than one thick, lumpy one.