How To Get Keywords For Your Niche

A keyword is a word or phrase people type in search engine boxes to find results for that particular word or words.
Before you begin writing and posting articles, you must get keywords that will enable search engines like “Google” to find your articles and place them on the first few pages of their results for those particular keyword(s).
For each article, you should generally aim to find one main keyword and one or two extra keywords, and you should use your main keyword once every 75 to 100 words so that the search engines can place importance on that particular keyword in your article, thus moving your article up in page rankings so website visitors can easily find you.
1. Find a topic, or “niche” for your website. It has to be a market that people are interested about, and there are literally thousands of them out there!
Here’s a great guide to finding one:

2. In order to get keywords for your niche, you need to familiarize yourself with what keywords are, and how to find them:

Go to Wordtracker Free Keyword Suggestion Tool, and enter the keyword toddler. You see the results are various keywords containing the word toddler and to the left of each keyword, you see an average of how many times people enter that corresponding keyword daily.
Choose a few keywords and proceed to the next step.
3. Once you have a keyword list, you need to put them to the “google niche keyword test.”Take one keyword at a time, enter it enveloped in quotation marks into the Google search box. If the results returned say 1 - 10 of about 1,000 to 10,000 results, then you know you have a keyword you can rank well in Google results pages for!For example:
If you enter the keyword “toddler” (notice the word is surrounded by “ “), you’ll see the results are: 1 - 10 of about 68,000,000. That’s way too much competition! Now let’s enter a longer, more specific keyword, “sick toddler.” The results are, at the time of this writing: Results 1 - 10 of about 9,970. That falls within the 1,000 - 10,000 range where we can write an article and eventually place somewhere on page 1 of Google and other search engines! This is the secret to how you can get keywords to make you successful.

the source:
http://moneystartsnow.com/how-to-get-keywords-for-your-niche/