Along with a bit of healthy research, there are some tools available to help you:
Answer the public – The auto suggest results provided by Google & Bing are a goldmine of insight for today’s marketeers. As you type you are presented with an aggregated view of the questions & therefore a hint of the motivations & emotions of the people behind each search query. This is a great tool to help you interrogate and help you understand ways to utilise your web content
Google Adwords planner – Plan your Search Network campaigns and learn what your customers are looking for. Keyword Planner is like a workshop for building new Search Network campaigns or expanding existing ones. You can search for keyword and ad group ideas, get historical statistics, see how a list of keywords might perform, and even create a new keyword list by multiplying several lists of keywords together. A free AdWords tool, Keyword Planner can also help you choose competitive bids and budgets to use with your campaigns.
Keyword planner – A keyword generator tool for Google, Youtube, bing and the App Store.