To all the guys out there, how do you deal with competition around the same girl?

Picture this, you're getting along pretty well with a girl (can be a co-worker, a girl in your class, in your group of friends...), but you can see that you're definitely not the only one having a good time with her or simply the only one interested.
How do you make sure that you come out as the guy on top in the end without using any fucked up technique?
How do you make better your odds without dragging anyone through the mud?
How do you make sure that she chooses the guy that's actually interested in her and not the guy who wants to fuck her once and never call talk to her again?
And all that without being weird as fuck, desperately trying to get some alone time with her, to kick anyone out of the discussion by being rude or anything...

To all the girls out there, if you see some guys competing over you, how do you make your choice, should you choose to?

P.S. Just to be clear, I'm not talking about competition at a party with your frat bros, trying to see who can bring home the hottest chick, nor am I asking any "pseudo-PUA" for shady ways to get dirt on the other guys and trying to hypnotize the girl.