Keyword research is the foundation of your SEO campaign.
I always start with a brainstorming session to list all possible words and phrases that people would use to find what I/my client has to offer. Remember to put yourself in the mindset of the potential customer. This is an important step and one that people try to rush through.
You know your product/service and target audience so your input here is invaluable. Ask colleagues and any customers that you have a good relationship with – different perspectives are always great.