1. Type the word which is related to your topic on google suggest
2. After typing that word in the search box, a dropdown list will fall with lot of keywords(and result volume) which starts with the word which you had entered in the search box.
3. select the low volume result keyword and check search volume for that in https://adwords.google.com/select/KeywordToolExternal.
4. check the same keyword in http://freekeywords.wordtracker.com/ also for getting search volume
After checking the search volume you will decide finally which keyword you want to target.You can also get keyword ideas from http://www.ask.com