Use Automated Bid Management Software
If you spend a large amount on pay per click search engines it might be a good idea to use an automated bidding and tracking tool. Tracking is a must if you are performing any type of direct marketing.
Chose Specific Keyword Phrases
You can lower cost and increase conversion rate is to choose multiple highly targeted words (or phrases) instead of trying to get tons of traffic with a single generic word like casino.
Split Test PPC Ads
Run A/B tests to continually improve your conversion rates and lower your cost per click. More info on PPC split testing.