Here is how I know I have the right keyword or keyword phrases:
1. The keyword actually matches current content on the website that can be further refined through content development
2. Market competition is already present in the SERPs (Search Engine Results Pages)
Tools that I use in keyword selection:
Its better to use more than one so you can reference each keyword or keyword phrase. Some tools offer more search criterias and others are just general and pertain to one market.
Every major keyword or keyword phrase should have a landing page. I dont suggest having more than two (2) major keywords and two (2) minor keywords and/or keyword phrase per landing page or else the Search Engines might get confused.
For any questions regarding keywords, please contact me.