A blog highlights your technical ability and showcases your ability to write blog posts. Your blog can be about different topics than those you write about for your clients. In fact, it should be on a topic that interests you. Visitors will see that you can not only write, but you can also build an online community. A good blog has the potential to earn you many referrals for more clients.
If you're at all interested in starting your own online business, there's no time like the present. We live in a golden age of wealth. As much as the media tries to glorify the perils of our society, we actually live in a time that's ripe with opportunity and the potential for monumental business growth at a scale never before experienced. Thanks to the internet and smartphones, the amount of commerce being conducted online has experienced explosive growth.
Don't use jargon. If you are offering technical expertise, include descriptions that appeal to your client base, not your peers. For example, if you are showing that you can code with PHP and AJAX, don't say "in this case, if the input field is empty (str.length==0), the function clears the content of the txtHint placeholder and exits the function." The person who needs you to work on their site will just scratch their head and say "huh?" Say, instead, "Start entering text into this field, and it will auto-complete."