# How do I approach drawing all of the possible constitutional isomers?

Does anyone have any tips on how to approach these types of questions? A specific example would be:

Draw all constitutional isomers of $\ce{C2H4O}$

I can get the easier ones like vinyl alcohol, but it's hard to get ethylene oxide and it takes a long time for me to get acetaldehdye. And how would I know if I got all of the possible constitutional isomers?