I believe the for the 172 it is reccomended not to lean in a climb below 3,000', many people confuse this with not leaning below 3,000'. If you are climbing higher than 3,000' it is reccomended to lean, after passing through 3,000'.

But remember, anytime you make a power change you should adjust the mixture, for the new power setting. The method I know (and this will help in complex aircraft) is if you are going to increase power, you rise from the right, meaning adjust mixture first, then prop (if you have it), then throttle, and you lower from the left if you aree decreasing power, adjusting throttle first.