One of the things you have to be careful about with Wordpress is picking a theme that doesn’t damage your search engine rankings. There’s a couple of things in particular to watch for.
Firstly, many free themes are provided with the condition that you leave the footer links intact. Trouble is, a lot of these link to sites in “bad neighbourhoods” – that is, sites that Google has banned, penalise or regard as junk. If you want to rank well and quickly, you don’t want a theme with shite links all over it. It’s worth paying for a premium theme or offering to pay the author for removal of the links. Some themes have “malicious” code embedded that add links or do stuff you don’t want. Be careful!
The second thing that is a problem is the way the header is constructed. Quite often developers embed an H1 and H2 tag in the header which is quite legitimate – usually for you to enter the name of your blog and a tagline. If you look up above, you’ll see my blog title and a tagline “A place to pontificate”. In this case, I made the title an image and removed the H2 around the tagline. The reason you don’t want your H1 and H2 tags here is that they appear on every page and you don’t want each H1 / H2 to be identical. Each page should have it’s own unique H1 / H2 tags.
Finally, a tip: look inside the theme files, most notably “header.php” for the code that includes the “sidebar”. You want this loaded last on your page as it contains links and stuff. For SEO purposes, ideally you want the text you post to be as near the top of the page as possible, so try and move the sidebar include code into footer.php.
It’s also worth editing sidebar.php to change generic titles like “blogroll” and “links” to something a little more relevant to the topic of the blog. Example, if you have a travel blog, then rename them “Travel Links”. In this case, I am using images instead of text so that’s irrelevant.
There are also some essential SEO plugins for Wordpress.