There are several simple but effective SEO tricks to optimizing a Simple Machines forum.
URLs
First, is the URL structure. Search engines value the descriptiveness of a URL. By default, SMF uses URL?s that are worthless for SEO. An SMF mod, called Pretty URLs, will rewrite your URLs to be far more useful for a search engine. Pretty URLs is very simple to install, but a common problem is to ensure that .htaccess is writable, and that the root directory is writable.
Notice the difference (these links all go to the same post):


Pretty URLs use the title of the post topic as part of the URL. This will help search engines to properly classify the page and build a stronger connection between the the page and the title of the post in search results.

Robots.txt
Next is duplicate content. Search engines will generally penalize the appearance of the same content multiple times. The interpretation is that the site is trying to ?stuff? in content to make the site more favorable for certain keywords. This is a problem because each message is individually accessible, as well as the thread, and then there is a separate view of the same content in a printer friendly format. What we want the search engines to do is simply index whole threads only, thus avoiding content duplication. All of this is easy to fix with a robots.txt file in the root html directory that looks like this:
User-agent: *
Disallow: /*?action*
Disallow: /*sort=*
Disallow: /*msg*
H1 Tags
Next is the H1 tag. Like the URL, H1 tags are used heavily by search engines to classify the content on a page. I have not found any SMF themes that take advantage of this fact, though I have not looked at more than 10 or 20. Unfortunately, there is no easy way to do this with a mod. It requires some modification of the theme you are using. Most themes have a navigation section that indicates where you are currently at in the forum. The objective is to modify the theme so that the end node (the current page) is wrapped in the <h1> </h1> tag. This will also require a change to the css stylesheet.
Google Tagged
Google Tagged is mod that tracks search engine referrals to various threads, along with what search term lead to the visit, and displays those tags in a tag cloud style box (Example). When visiting a thread, it will also show what search terms have lead to that thread in the past at the bottom of the page (Example). It is not pure SEO, but it does reinforce keywords with the search engines.
Meta Tags
Meta tags are another tool that search engines use to classify sites. Edit the ?meta description? in the index.template.php file to describe the site. Users of SMF version 2 can use the vBulletin Style Meta Tags mod to update the tags based on the thread that is being displayed.
Header and Footer
For an easy easy way to add content to the header and footer of an SMF forum, use the Global Headers and Footers mod. Descriptive text can be an essential element in search engines properly classifying the contents of your forum.


Source: http://www.jerry-bell.com/search-eng...achines-forum/
Leg!on Reviewed by Leg!on on . SEO Tips for SMF There are several simple but effective SEO tricks to optimizing a Simple Machines forum. URLs First, is the URL structure. Search engines value the descriptiveness of a URL. By default, SMF uses URL?s that are worthless for SEO. An SMF mod, called Pretty URLs, will rewrite your URLs to be far more useful for a search engine. Pretty URLs is very simple to install, but a common problem is to ensure that .htaccess is writable, and that the root directory is writable. Notice the Rating: 5