There’s really just two rules:
1) If I have an edge – take a position.
2) When the edge is no longer there – get out.

It doesn’t matter what my entry point was and it doesn’t matter how much I’ve gained or lost on the trade. When the edge is no longer there, I shouldn’t be either. And when it is there – I should stay in the trade. This actually requires some discipline because there’s always a temptation to bail when it begins to go against you and there’s also always a temptation to try for too much when things are going your way.