A therapist is very useful. It is difficult to see yourself clearly from the inside out. It's easier for someone from the outside to help you spot patterns, then you will gain some level of awareness of how they arise in your life (because you will be discussing your life with the therapist).

The paper I link to on dreams should help too. Dreams are sort of an internal mini-therapist, but again, it is easier with an outside perspective.

The first step is to consciously notice the pattern - at first it may be difficult and you would notice it only after the fact, but with some introspection and training you can generally also learn to notice and acknowledge it while you're in it. When you do catch it with your "rational brain part" it's generally not that difficult to break it.

That's a big part of what cognitive behavioral therapy does. Also, mindfulness meditation is one way for doing this that helps some people with the "catch yourself doing that pattern" part.

Journaling or therapy can be effective strategies. Both give you the outside perspective needed to spot patterns.