Search Engine Optimisation, or SEO is the process of improving the ranking of your webpage on the Search Engine.
SEO is generally quite intuitive, if what you are writing is relevant to a subject, there is a higher chance that it will be ranked higher on the search engine results of the subject. It's logical, because a search engine that returns the most relevant results is deemed as a "Good search engine", so Google and other search engines will want to tweak their search engine algorithms to find the "best" results.
Having said this, please don't go about extensively spamming the same few words in your blog (you know what I mean if you stumble upon porn sites - they abuse all sorts of variation of the same word). Search engines generally blacklist these sites and prevent them from appearing in search listings.
For casual bloggers like us who wants to increase traffic via search engine, here's a small thing you can begin with.
Your blog has 2 unique IDs, your name and your blog's name. Should past visitors want to visit your site but forget the name, they might type the any of them in the search engine. In my case, typing "Shingo T" and "Cup of Ice" currently brings my webpage as the first entry in Google's search page. If you are using names like "John" and "John's homepage", chances are that it will be tough for people to find your website.
But of course, most people out there do not know who the hell "Shingo T" and "Cup of Ice" is, so they won't even bother searching using these key words. That's why if your blogging revolves around something specific (eg. fashion or dog grooming), have that word used as a title on your blog.
For instance, someone may name her site "Globetrotter - Addiction of a Travelholic". One look at the title and you know what the blog is about. So chances are that this will attract someone looking for travel blogs, rather than someone looking to recover from nicotine addiction.
For those who are more technically savvy on webpages, you can read this free document from Google on SEO - Google's Search Engine Optimization Starter Guide!
And finally, never let traffic take the fun out of your blogging! ^_^