I have a lot of trouble determining when I should talk to a girl and when to not talk to her or freeze her out.

This happens a lot to me. For example, when I see her talking to other guys I tend to just freeze up with jealousy and ignore the girl completely instead of trying something else.

There's no right or wrong time, just talk to every girl who you find attractive am see if she lives up to your standards. If not keep it moving. I just recently started approaching girls even when a guy is right there. I saw this one girl an I could tell the guy she was with was not her boyfriend so I said " you know what fuck it" and it went extremely well. Too bad for that guy. Anyway just push your limits bro. Do things you wouldn't normally do.

For example: once I talked to the girl with a guy there it became a lot easier to approach I girl that's alone.

Approach a hot girl with a big booger on your face, now whenever you don't it's Eaiser. You get the point. Lol at the booger thing. I'm sure it would work tho