graphix,
Risk management is the cornerstone of all successful trading. I never put more than 1.5% at risk on any given trade, and I never have more than 10 trades going with risk to original capital. In theory, if I were fully exposed to a downdraft like todays, I would not lose more than 15% of my account. Now once I move my stoploss up to breakeven, which I try to do quickly if the trade moves in my favor, I can invest more capital. The goal is to have as many open positions as I can create that have no risk to original capital. In a trending market I sometimes use all my capital, all my margin, and start buying options to increase my leverage further. It is a bit like shooting craps. Once you hit your number and get your money back, it often pays to let it ride. Eventually you crap out (or get stopped out in the case of the market), but sometimes you can really make a bundle. For instance, I was up 30% last January.
To answer your question more directly, I don't limit long or short positions to any fixed percentage. If the market is trending downward, I will load up on short positions, and if the market is trending upward, I will load up on long positions. The puts I bought today were the first short positions I have opened since last August.
Those puts I bought this morning were entertaining, but I didn't buy very many of them. I probably put less than 1/2% of my capital in them. Although, it was really cool to see them more than double today. Makes me wish I had really loaded up -- well, not really, the risks are too great, but it is fun to fantasize.