It depends on your content and keywords you want to optimize your website for them. you can use of your competitor's keywords too.

Choosing the keyword starts with Identification. You must first create the list of keywords. These keywords should be more closely related to your topic or product. Keep your mind like a visitor and list down the possible set of keywords that you will use or search in order to arrive to your page.

first page is all that counts! the rest it's a lost of time

When doing your keyword research, don’t focus your efforts on keywords with high total searches per month. The majority of keywords with large searches per month aren’t necessarily buyers. Longer-tail keywords, or more specific phrases, often get less searches, but have higher conversions because the consumer tends to be looking for exactly what they are going to buy.To find new keyword ideas, visit: Google® Keyword Tool

You can do it with the help of Google keyword suggestion tool.