1) have a good and well polished game.
2) have a better website (seo, keywords, buy information...)
3) have a press release on that website, featuring screenshots.
4) contact review sites, give them a free version link.
5) distribute a pad file.
6) post on gaming forums.
7) put link in your signatures.
8) buy some backlinks to your site or do banner exchange.
9) google ads if you want (but with careful selected keywords (dont use something like 'download free game' those people will not buy your game, use 'card game' instead.
10) good luck!