Requesting a link exchange in link farm is easy. But I seriously doubt that Google consider it. The question is, how to successfully request a link exchange in a decent site. Normally, these sites have a better PR and enough visitors.
If you want to exchange links just ask the category and Pr of the page you wish to link .Decently mail the webmasters of the site so that you can specify whatever the qualities you want to exchange links.
Be personable and promote conversation, not your site shamelessly. Show them that you have looked at their site, and the benefit it would have for them. Keep it short & simple (K.I.S.S.), don't overwhelm them, and don't be desperate.
you can use this forum or use sites like: link2me.com linkmarket.com or the automated ones like gotlink.com
When requesting for a link exchange write a formal letter of link exchange. Thru this, webmaster will see sincerity in your link exchange request. Plus, dont forget to mention where you want to put your link and where you will put his link.
link2me or linkmarket gives you only very bad link partners. Most of them are too low pr or are bad neighborhoods. Don't link exchange within these services and you will be hit by search engines. The best way is always socliciting honest webmasters for links.