It's subjective
This is what has worked well for me, of course, it is extremely subjective.
1. Stay the fvck away from negative people. Unfortunately, through the process of finding guys who can teach us a great deal we will encounter some guys who have serious interpersonal skills issues. If they regularly crash your state, then it's time to put a lid on them and go solo or out with someone else. Fortunately, when you bring the A game attitude, most women will be a blast to interact with and the few negative ones are usually just a false front to not look easy.
2. Knowing that women bring a different mindset, so you don't trip into the trap of believing it's real. Women are unconciously motivated to seek a better man, and that's the only reason she isn't plopped on a couch watching Flava Flav or something. The idea that women just go to loud bars/clubs to talk to friends is totally insane, that's the worst place in the world to try talking. They go to quiet, small places when that is true or a restaruant (not that you can't manage to approach them anyway).
3. Breath Deeply. I think this works well for me. If I start to get dressed, I breathe into my stomach (you should feel it push out) slowly a few times. Should work in just a few breaths.
4. Mediatation: If I am feeling really aggitated one day, I will do meditation. It can be a pretty big stress reliever. I use guided meditation mp3's. I posted a link to a free one not long ago.
5. Just being around positive people and remembering a time when you were really fired up about going out to meet women. Work yourself into that state. Run around the couch a few times if you want.
6. Talk your head off: Get a job where you talk to people all day long. This helps more than anything else I've ever tried. Esp try to get jobs where you have to approach strangers. I easily did thousands of approaches this way in a reasonably short period of time resulting in uncountable numbers of lengthy conversations. 6-12 hour days mean this can add up fast. It helps greatly.
7. Jam out in the car/ while getting ready. I don't know if it really helps but it's fun.
8. No thinking about approaching. Walk in and get a couple down the hatch. The waiting, thinking, hesitating is a state killer for me. I immediately go approach when a wingman starts hesitating. Often when they are having trouble, they will try to get me to hesitate too making some excuse why not to approach. All this will ever be is an excuse. I always approach to get myself out of that situation. If I came to approach, then I want to actually approach not debate. If it's a frequent problem, see #1.
9. Address insecurities before leaving, block out what crops up. I make up my mind that I won't think about this stuff, I try to make sure my clothes, hair, etc is in best shape before leaving so I won't worry about it. If things are less than optimal, then I just have to block that out and not think about it. Just decide I have what I have and should/wish/wants don't matter now. Just see what happens. Life is an experiment.
10. Approach the girls I actually want. In any place of even only a few people there should be someone I'd like to talk to. If there is no one, then I need to go someplace else or stop making excuses. I don't force myself to approach people I have a bad vibe about anymore. At the same time, if I have a bad vibe about 300 people in a club, then I know this is an excuse or I have walked into a gay club, one of the two.