One way I've found that helps me psychologically is to look at the portfolio performance of my open positions everyday. I love seeing open profits, hate seeing open losses. When seeing most of my positions in the red, it would always gnaw on me, yet I just couldn't bring myself to sell (or cover in the case of short position), hoping that the losers would come back at least to break-even.
But one time when I was fortunate enough to have a few winners (not my own ideas, but still they were my trades of course), I decided to try aggressively selling losers and adding to winners. And I found it to be psychologically rewarding. All of a sudden my portfolio was showing more green than red and the net portfolio value started rising instead of falling.
Not to say that I would recommend doing this in a haphazard way. Always have a stop when you open a trade, whether hard or mental. Then move the stop to break-even as soon as you have a decent gain, to prevent a winner from becoming a loser. Never risk too much on one trade, etc., etc.
Another technique I've found helpful for a position that is only a slight loser is to write a near-month covered call. That way I have a little downside protection and can turn a loser into a winner without taking the excess risk of doubling up. Of course one still has to be disciplined enough to liquidate the combined position if the loss starts accelerating.
I still have a lot of obstacles to overcome in my trading. For some reason, I find it much easier to be disciplined with individual stocks compared with indices. The constant chop and noise in the indices always seems to shake me out at the wrong time.
Anyway, just thought I'd share this in case it might be helpful to others like myself who are still struggling with trading discipline. Sorry if this stuff is too basic for the pros here.
TechSkeptic