One of the easiest and most effective ways to maximize ROI on your website is to simply use the website the way that it was built to be used. Simple things such as updating a blog, making tweaks to content based off of web research, and keep a website updated with the latest news and events are all ways to maximize your return on investment.
It is also a good idea to track conversions to determine how much business is coming from your website vs other various means of marketing. A lawyer that we met once did this and found that his website was producing 25% of his new customers!