The most effective sketches rely on best methods used by players. Allow as much detail as possible in the allotted time. Drawing too fast will just make the sketch incomprehensible. By selecting an appropriate color you can maximize chances of getting your clues understood and the players guessing the word. A black circle with lines around it could be a spider.
Color can effectively get a message across.
Show the opposite to clarify what aspect you're after. Then cross out the shorter figure. Draw something that sounds like the word. To indicate a rhyme, draw an ear. Then draw the rhyming word.