Don't worry about what culture says, be yourself first and foremost - if you are a nice person then don't pretend not to be - however you do need to bring challenge, intrigue and excitement - that's what the bad boys bring, until it all goes wrong... In any case you want a quality woman not one that settles for bad men. Be intriguing, be a challenge, and be exciting - in your own way.
If you feel you have to address your weight then say you are looking to get fitter or something, and make some changes. But if you need proof that size doesn't matter take a stroll down the high street and see how many chubby blokes have women with them.
There are nice and nasty women everywhere and you won't be able to tell them apart until you speak to them. Do things that you enjoy and talk to the women you meet there.
Talk about your hobby but in terms of your emotions, motivations and your character traits - nobody's interested in the stamp collection but they are interested in why you've got one, what it brings to your life, the thrill of hunting down a rare stamp, the other crazy stamp collectors you meet, whatever it is you have to talk about it, if it's something you enjoy then it's a great thing to talk about.
If you are getting rejected then congratulations, you are doing better than those that aren't even trying. I'm sure that half of those rejections you would have rejected them first if you had options, so your rejection number has now halved just like that. Go into it expecting to have to pass some sort of test and this sets the tone straight away that you have something to prove... You should feel that it's you that's doing the qualifying, check them out, ask them questions and, every now and then, treat their answers like it makes you not sure about them - if they are an English teacher then you aren't sure about them because they manage to suck all the fun out of a great book - things like that. Make (fun) assumptions about them and let them tell you if you are right or wrong.. Obviously this all needs to be done with a smile. If it helps, go into each date thinking it's just a bit of practice for you for the next one. Your goal is to go out, meet someone new and learn something from them - if that's your goal then you'll always meet it - whatever happens afterwards is irrelevant.
Good luck.