By far, the most important aspect of search engine optimisation (SEO) is the use of keywords. In a nutshell, a keyword, or keyword phrase, is a word or a series of words which have great importance or significance and have two main functions: to show both your customers and the search engine crawlers what you and your business are all about. Typical keywords will summarise / detail your business functions, or important products which you supply. A good way to consider if you have chosen the right keywords for your SEO is to think about what your customers would type into Google if they wanted to find you. Your keywords should match your customer’s searches.
The infogrpahic below is from the folks at Promodo and details a step by step approach to keyword research: