The good news is that, as far as RRSPs are concerned, fairly simple fiscal planning can go a long way. The key is to compare your present (or contribution) tax level with your probable withdrawal tax level.
Because taxes increase with your income level, ideally, you want to contribute when your income is high and withdraw when it is low. In the same fashion, you want to avoid unnecessary contributions when your income is abnormally lower and limit withdrawals in periods where your income is higher.