if you are gonna use it for spam then its pointless to even start. its not effective anymore because everyone else is doing it. also it will not give you the link juice you are looking for because the url's are shortened.
You can search for people tweeting about topics you are interested in (ex poker) using advanced twitter search. Interact with people on twitter, give thme advice. DON'T hard sell. If they're interested in you they'll follow you and if they're curious they'll check out the link to your website that you put in your twitter profile
Twitter can drive traffic for your site but remember you need real relationship with your follow to make it more successful.