I think the first thing you should do is to think about why non-vegetarianism (i.e. killing animals and using them as mere commodities) might be wrong. Animals are sentient beings just like humans, meaning that they can suffer and feel pain. When you look at the biology and genetic make-up of animals and humans, you might realise that there are no substantial differences that sets us apart. So in the big picture, we are the same. And since it's generally considered to be wrong to use violence against humans, then violence against animals must be wrong also. However, if being violent against humans is somehow acceptable, then you cannot use the above argument to show that violence against animals is wrong.
To answer your question, I would suggest joining up with animal rights organisations in your area. Help them do leafleting, give out free violence-free food, write letters to newspapers to argue the case for vegetarianism and respect towards animals, to politicians about food labelling laws, and to food companies about getting more violence-free options. In short, the challenge is to educate the masses of non-vegetarians, not to coerce them. And while slaughterhouses are extremely dirty and evil businesses, they simply fill a demand from the masses of the uneducated and uncaring.
I no longer post here after VB was sold in 2012. (See my profile page for details.)