Depending on what state you're in it may differ. In Texas (and a number of souther states) for example, if you make eye contact with someone on the street, it's usually common courtesy to do a little nod at them for acknowledgment. If you're crossing a road on foot, or waiting to cross a 3/4 way in your car, and someone stops and says you can go, a simple wave saying "thank you" is always nice.

Most people I've run into respond well to either, "Hey, man...." (best used for casual conversation for people teen to 30ish) , or, "Excuse me, sir/ ma'am" (for business/ professional related conversations or for people over 30ish. Also good for talking to people in a uniform such as a police officer).

If you are meeting someone for the first time (particularly if you are being introduced by a third party), you'll usually shake the other persons hand and say your name (the firmer the grip the better).

If someone talks about a subject that you know something about, don't stay silent. That just makes you come off as a third wheel. Chime in (try to wait until one person is done talking since interrupting is usually not a good idea) and say what you want to say.

If you know nothing about a subject, then try to ask a question about the topic (don't lie to much, since blatant lies are easy to catch onto).

The easiest way to learn how to be more social is from trial and error. If someone makes an ugly face after you say something or they say something mean back, don't say it next time, or say it differently. Just because one person thinks your "weird" ain't the end of the world. Hell. Every one I know thinks I'm weird (and I am lol).

If someone gets angry and you don't know why, it's not always bad to apologize for nothing. Deescalating an issue is better than getting into an unnecessary fist fight (although they can be fun to win).

Google may help you come up with other ideas about how to improve.