A trait of pretty much all the people I know who society would view as "very successful" is they seem to do this automatically all the time. Their confidence gets them into higher profile situations where there is opportunity to succeed and once there their mindset maximizes their chances of doing so.
A trait of the few people I know who I'd describe as "exceptionally bright" is they don't do this because they are too aware of their limitations.
People who fit into both groups I think are rare ... and quite something.
People on the subway grating on my nerves? I pretend I'm someone patient. Need to bang out a particularly annoying task? I pretend I'm someone who's really interested in that task. Wife irritated by my sloth about the house? I pretend I'm someone who cleans up promptly. Feeling particularly miserable today? I pretend I'm someone who's naturally happy.
It doesn't work forever, and it doesn't work perfectly, but it works better than any other mental trick I've discovered.