There are many different methods to obtain quality backlinks to your website. You will find that some methods work better than others depending on the subject and popularity of your site.

Directories

Submitting your website to directories is one of the best ways to increase your PageRank and even get some traffic at the same time. But submitting your site to just a few directories won't be good enough. You need to sit down and spend the necessary time to submit your site to a large amount of directories. This may seem like a painstakingly long process, but you'll be glad you did it when you notice results. I have taken the time to make a large list of free directories with high Page Rank. Although directories with low PR may seem like a waste of time, you should submit your site to them too because it still helps and they could eventually become a high PR site which charges money to submit to.

Link Exchanges

A very common practice to improve your Page Rank is a link exchange. This is simply where two people link to the other person's website. It's best that you only link exchange with someone who has at least as much PR as you and the subject of the two websites are similar. If you receive a link from a website with a subject which has nothing to do with yours, you'll find that very little if any PR will actually be transferred to you.

Forum Signatures

If you are an active user on a forum or message board, it would be wise to put a link to your website in your signature. This could help improve your Page Rank if the forum has a high PR, it could help improve your traffic from the forum members seeing your signature, and your site could get spidered more often because it is linking to a forum.

Buy Advertising

Although it isn't the best of choices, many webmasters will buy text link ads on websites with high PR. Although this can be effective, it can be very expensive and only a temporary thing. If you purchase text links for just a couple months, after the months are over you won't have the backlinks which were giving you the "votes" you needed to keep your Page Rank. So you have now spent a large amount of money on text links, but in the end you're right back where you started.

Articles

This is a method which not many people know about. Basically, you write articles about the subjects you know a lot about. You then let other people use these articles as long as they provide a link back to your site. If you wrote a quality article, you'll find many websites will want to use it, thus giving you plenty of backlinks. This method can work well with anything which you develope and give away for free such as scripts, web design, etc.