Before moving on to choosing your keywords, you should first be able to know who the target of your PPC campaign is. You should know where your ideal people live, why they need it and an overview of their frame of mind.
A tightly defined audience will help you in the long run.
Google has a feature which will enable you to block up to 5000 websites from running your ads. This will help you control where your ads appear and block those irrelevant to your campaign. It will need time and effort but consider it a good investment as it will give you more quality leads.