One of the easy things you can do is disable and clear the Site Log. Since most sites use Google Analytics, this feature is rarely in use and simply takes up space and consumes resources. In many cases, it can also slow down a site dramatically. The Site Log will need to be disabled in both your Host Settings, and your Site Settings. Then, run the query below to clear out the Site Log on the database.
DELETE FROM [dbo].[SiteLog];
...or in the Host > SQL module...
DELETE FROM {databaseOwner}[{objectQualifier}SiteLog];
Next, for the same reasons, you will want to periodically clear out the Event Log. However, in many cases you will want to leave a certain amount of existing records, or export the log to another database if you need to maintain that information. The query is very similar:
DELETE FROM [dbo].[EventLog];
...or in the Host > SQL module...
DELETE FROM {databaseOwner}[{objectQualifier}EventLog];
Finally, something that comes up occasionally, is that your search index might fill up. You can save database space and increase performance by running
a specific set of queries to clear your search index.
That should get you up and running today, but in the end, you will also want to audit your site to determine where any performance enhancements can be made and where. A great place to start is the
DotNetNuke Performance Best Practices Guide by Mitchel Sellers.