Read and comment on blogs that have content similar to the content on your website. Add a link to your website at the bottom of your comment.
Write to blog owners with highly ranked blogs in your niche. Ask if you can write a guest post that links back to your website. Write good content for the guest post to entice readers into clicking on the link to your website.
Sign up for social bookmarking sites. Upload a description and a link to your website on these sites.
Create several websites with relevant content that link to each other over time. Ensure that all the websites have valid, useful content.
Pay Google for online ads that have links pointing to your website. This is a quick way to get backlinks if you need some immediately.