i am using a keyword planner....

First find top competitors of your niche, than track keywords for which they rank on top on search engine, repeat this process for multiple competitors and combine all those keywords , finally you will have keywords which are already in use.

Use LSI keywords from google to extend your keyword research.

To finding keywords you choose by google keyword planner or google auto suggestion.

Im using a keyword planner.

Google keyword planner tool.

you are using a keyword planner.....

no doubt Google Keyword planner tool is best for keyword research . but before choosing keywords you have to think how much its effective for your business. and what other keyword your competitor is using.

keyword should be relavant to the website one can analyze through the keyword planner