Include your website in every email you send!
There isn’t a better opportunity to get your website out there than this. It's free and effective, and anyone getting in contact with you will know that you have a website. What's more, search engines will notice this as well!
Here is a quick example:
Generally, you can edit your email signature through your email provider's "Settings" tab. If sending email from your mobile device, you'll have to update it through your phone's "Personal Settings" as well.