I try to focus on the things I have 100% confidence in. I never feel 100% insecure, however there are parts of me that can become attacked. Lets call them personal weaknesses. Those things I know bug me and I assume, during duress, are why people are breaking up with me (one of the few times I feel very insecure)
I do have insecurity that comes in waves, but I have two women who like to stroke my ego so its hard to ever get to hard on myself. I recognize these happen during rough times. Crappy week at work etc. I try to head them off, but I am human so I sometimes fail. Insecurity for me almost always leads to self doubt, which creates its own problems.
I know this is a technique someone here expounded a while ago, I like it, but haven't had to use it. Make a list of all the qualities you love about yourself, and then a list of all the things you like. Keep the 2 lists for when you feel an "insecure" day.