Same as arebelspy.
1) Set your target asset allocation and rebalancing bands. Write your plan down and stick to it.
2) When you make new money, buy the lagging asset(s) to keep things as balanced as possible. Depending on the transaction fees, you may want to pool up enough cash to buy in larger chunks.
3) Once or twice a year, check the percentages. If you hit a rebalancing band, sell some of the high asset(s) to buy more of the low asset(s) to get back to the original target.
Generally speaking, your goal is to rebalance as little as possible to avoid capital gains taxes and transaction fees while staying true to your original allocation.