I've spoken to a colleague who has quite a lot of experience in this area (although I wouldn't call him an expert!) and he's made a few suggestions which I think have been quite helpful:
SemRush is pretty easy to use and free, and it shows you the top three keywords that your site ranks for, and you can also check out your competitors too. I've looked at this and have written my blogs around the results but it does seem to change quite often which I guess is where adding regular content comes in.
Google Keyword planner:
This is meant to be the holy grail of SEO but I haven't yet spent enough time there to understand it fully. I have a Google account and have signed up but haven't yet managed to have any luck with any results without Google calling me to try and take my money! Has anyone else had any luck there?
To be blunt, put yourself on the other end of the keyboard. If you were looking for your product what would you search for? Sometimes people try and get too technical and think too much out of the box which ends up over-complicating the whole process. Use your common sense and put yourself in the mind of your target market to come up with the best search queries.
Apparently something like 80% (don't' quote me on that, but it is high!) of internet searchers type a location after their product search. Even if you have a service which can be provided remotely such as web design or copywriting, people still like to do business locally. Consider putting your home town, city, and state in your copy too.
I know that increasing your SERP ranking is a lengthy process and updating a regular blog using relevant keywords definitely helps. but does anyone have any more tips for hot to make sure that the right keywords are in your copy and online content?