I'd say that the number one thing that helps me, other than being aware of the probabilities of up/down movements like haejin prescribes is simply to not have too large a % of your total stack in any one trade.

This is counter-intuitive to everyone (myself included) who likes to see their whole stack increase by 50% on a good trade, but it's nearly impossible to get rid of the FOMO and FUD that accompanies such a large gamble. I find that in the long run I'm more profitable by making an educated decision then sticking with it since I'm no longer worried about losing the shirt off my back the second the trade doesn't go my way.

Of course, methods that increase your ability to hold are more advantageous during bull markets. Unless you're a proficient trader, simply sitting on your stack and not entering the market is a perfectly viable option during bear runs.

edit: A simple reminder from someone who's way better than I am....
https://imgur.com/iz2fctH