Quality not quantity is what matters.

If you place a link that is in a place where no actual real person would ever click on it you are just leaving a footprint for the search engines and doing yourself no good.

I have sites ranking in the top 10 that have less than 100 backlinks.

It's not a quantity game.

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Like the others said.

Plus participation in Social Media sites and other forums, find a subtle way of letting people know about your forum whilst providing something useful to the post that has meaning. Keep it relevant to what your aiming for...

Then Articles, Press Releases, Social BookMarking (wont have much effect if you bookmark your forum the one time unless it goes viral or until you create more forum threads with activity) Videos, PPC (bit extreme though lol) Free classified Ads, Social Networking blogs, host a Blog aiming to get your users to the forum and theres more...

Try something unique and set yourself apart.

Well, There are lots of ways to get more backlinks. Such as blog commenting, Social bookmarking, Directory Submission, Article Submission, Using web properties 2.0 to publish content and etc. However, If you can make sure that you are getting backlinks from the sources which are related to your niche, that will be more helpful to you to increase your SERP on google as well as PR too.

Create quality of inbound links. Google gives more value on the quality compared to those irrelevant sites that you are getting. Google gives more value on DoFollow sites as well. Then quantity after quality.

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I'm a newbie also and just started learning about SEO. They said that you must build a permanent links to benefit your site for a long run. Adding links to your signatures is good and also submitting your site to directories. Actually, you can google it to find many tips on how to optimize your website. Just read and read... goodluck!