Find and add users that are related to your niche. Be informative and helpful and drop your link every now and then. The goal is to seem like a real person and they follow you try not to spam because users will stop following you.
1- search for a keyword related to your business, and use (-http before the keyword ) example: -http make money online 2- start reply for every tweet with your promotion and your site you even can get 10000's of visitors from twitter without even using twitter.com and for free, i have explained everything in my latest report
Your success on twitter will greatly depend on your niche. In some niches twitter will be gold, in others it will be completely useless. In general, if you cannot see how twitter will build value for your niche, then it probably won't.
Good thing to start is make promo that when your customers and new ones are following your site, they will gains something.