Here're some free Google tools to help you build an effective keyword list:
- Keyword Tool helps you generate keyword related to your products and services. The tool gives competitive analysis on each keyword, local and global monthly searches for keyword, and local search trends. And even without entering any words or phrases, you can look at potential keywords by category. You can add these terms to your keyword list and also decide on match type before adding them to your account. It's easy to streamline keywords based on location, language and devices (Mobile search).
- AdWords Traffic Estimator gives estimates about cost-per-click (CPC) bid for your keywords. Clicking "check estimates" in Keyword Tool, take you directly to Traffic Estimator, where you can check metrics such as estimated average CPC / ad position /daily clicks / daily cost. Google Grants accounts have max CPC bid of $1, you can define that bid before generating estimates.
- Search-based Keyword Tool pull up exact search queries users enter pertaining to a particular product or service. Apart from helping you get more keyword ideas, this tool gives you ideas about negative keywords if you see any irrelevant search queries triggering your ads.
- Google Trends & Insights for Search tool can give you suggestions about keywords rising in popularity, search trends from specific target locations, and time period during which you might run a campaign.