Most of the time this means I can revert my working copy to rev 12345 with this command:

svn merge -r HEAD:12345 .

The merge command requires a directory parameter, the dot just means the current directory. This only reverts your working copy though, so don’t forget to commit after merge.

Reverting back to a previous version is one of those things that I do infrequently enough that I end up searching for how to do it each time. Perhaps writing about it will help me remember this a bit better. If nothing else I know where to look for a quick example now.