How can I not be a pushover?

Well we would likely need more info as to why you think you might be a push over. But in general, if you typically do whatever people ask of you (even if you don't want to) or if you continue to be nice to people who are mean to you on a regular basis, then you might be a pushover.

No need to be a jerk or rude to people to stop being a pushover. But if someone asks you to do something and you absolutely do not want to, then do not be afraid to say no. If people are constantly mean to you, don't be mean back, just hang out with other people.

I think the gist here is that if you don't want to do something then don't. Don't be afraid to say no to people on the chance that they might be disappointed. I'm sure you'll figure it out.

The biggest mistake that people make in this situation is thinking that you need to be a jerk, or overly aggressive and picking fights in order to not be a pushover. This isn't true at all, and if you start acting like that, girls will just think you're a hothead.

The best thing to do is stand by your convictions and make sure that you take some opportunities to do and get what YOU want, even though maybe someone else has a difference of opinion. There's no need to ignore other people's opinions, but defend yours and if it's something important, stick to your guns...without being rude about it, of course.