Long-term Investment Portfolio Rebalancing Strategy

A few questions I'd love to hear people's thoughts on.

1. Once you decide on your portfolio allocation, what is your rebalancing strategy?

I am inclined to rebalance somewhere between periodically (every year or few years) but also looking at thresholds to determine when to rebalance. I would love to hear your thoughts and how you decide to do this.

1. When you do decide to rebalance, do you sell high performing categories to purchase low performing categories to rebalance or do you simply divert your NEW incoming money accordingly to the under-threshold categories? Pros/Cons? At what frequency are transaction fees negating this?