The ranking of a website in Google contributes greatly to the commercial success of a site. Get your Google words right and you could find your website on in Google's top ten returned searches - and on the internet, that's gold.
The key is to find the most searched terms on Google for your chosen subject (whether that's a commercial or leisure endeavour). There are a number of online resources that will help.
Start at the horse's mouth, so to speak. Google Adwords allows you to search enter in as many 'searched terms' (what you think your potential audience will type into Google). So, if you were writing about insurance, which at the moment is one of the most competitive commercial search terms, you might enquire about the term 'insurance' and any related terms you can think of (eg car insurance, insurance quote, insurance Stockport and so on). Leave the 'Use synonyms' box checked and see what Adwords gives you. The list of Google words returned to you will help you to make a list of keywords you can use as a base from which to start writing your optimised copy.
There are lots of free keyword generators on the internet. Just type that in to Google and you'll find plenty. Free Keyword Discovery is pretty good for starters.