Don't go fishing while your house is on fire
Well, don't. Your house will burn down, and you'll have nowhere to cook your fish (if you catch any). You should put out the fire in sente and then you will have time to go fish.
Alex: Although this page is humour, it is a real proverb (at least, I've heard it used as such, and use it frequently myself in reviewing kyu players' games). For the metaphorically-challenged: it's similar to but slightly more specific in meaning than the oft-heard "urgent moves before big moves." I say more specific because it usually refers to (or, at least, I usually use it to refer to) the bad habit of playing moves that only take territory, when there is some crucial tactical situation like a running fight that you should be getting your attention.
tapir: Probably "Don't drink coffee while your house is on fire." is more suitable for western readers. See: coffeebreak moves
I think Western readers are familiar with the concept of fishing.