It depends what you're after.
If you want to get a girlfriend, just be yourself. You can't change who you are. That doesn't mean, however, that your (future) partner can't bring out the best in you. If you can't be yourself around your partner, guess what, your relationship will NEVER last. EVER. EVERRRRR.
On the other hand, if you're just looking to score a girl to 'have fun' with, you can try using a different approach, if being yourself doesn't do the trick for you.
If you want to pick up a girl, there's just a few minor tricks that will help the girl like you more:
- Make sure you compliment the girl at the start of the conversation. This does not mean, however, that you're supposed to run to the girl screaming "OMG YOU'RE SO HOT, I WANT TO HAVE SEX WITH YOU". It's good to be straight-forward so that the girl knows you're into her and that she realizes your intentions, but the approach I listed above might scare her off, haha. I would say something more in the lines of: "Hey, do you know where the nearest strip club is?" And follow up by telling her "Sorry, I'm just messing with you. I thought you were cute so I had to stop you."
- BE CONFIDENT! I can't stress this enough. You have to make sure the girl knows what your intentions are and therefore it's important to be confident. If you're looking down at the floor the whole time, she might start thinking you're hitting on the floor, instead of her. Eye contact, body language, touching, ... Pay attention to these things and you'll be just fine.
- Try to implement the 'US-mentality'. And by 'US' I don't mean the United States, no, I mean 'US' as in 'me and you', 'we'. This will show your intentions to the girl even MORE and will make her feel more comfortable and more able to grasp what's going on. Let's say you're looking for a place to party, when suddenly you see a really cute girl. Naturally, you walk up to her and start talking. In the end you'll be wanting the girl to go with you, so instead of asking her where's SHE'S going tonight, you ask her "So, where are WE going tonight?". This is just an example, but try to use the 'US-mentality' at all times.
- Seal the deal. This doesn't mean you have to get her to come to bed with you the first day you meet (ideally, this would be the case), no, just make sure you can contact her again in the future. Ask her for her number, ask her out on a date, ...
- Don't give up. Sometimes you'll get rejected. There's nothing wrong with getting rejected. It happens to the best of us j/k ;-). However, it's important to be persistent. Show the girl you're willing to fight for her, even if she's surrounded by her friends, be it male or female.
Well, there you go, I hope this helps. Other than that, it helps to have a sense of humour and a certain level of attractiveness, haha.