If you are in WordPress.com, you cannot and need not do much to improve the SEO technically as it is a great platform for SEO already.
Still, here are some ways for better SEO in your WordPress.com blog:
* First, make sure that your blog is set to allow search engines. Visit Settings – > Privacy in your dashboard and choose the first option.
* Register your own domain name and host it with WordPress.com instead of having your blog as a subdomain . Having your blog in your domain name is good for SEO and brand building.
* Register with webmaster tools provided by major search engines and follow the insights provided by them. Visit Tools – > Available tools in your WordPress.com dashboard.
* Tag and categorize your posts with relevant keywords so that you get listed in global tags pages in WordPress.com. Getting listed in global tags pages can send you direct and search engine visitors.
If you have your WordPress blog self hosted like ours, you can have absolute control on every aspect of on-site SEO.
Please note that search rankings are calculated from a combination of over 200 paramaters and what you do above is only on-site paramters that you can control within WordPress.com . Write quality content regularly which will attract high quality backlinks and participate in your community genuinely. Track your stats and improvise. Only this holistic approach will ensure that you improve your WordPress.com SEO.
Update: Please check the official SEO guide from WordPress.com