Create a git clone of that includes your Subversion trunk, tags, and branches with
git svn clone http://svn.example.com/project -T trunk -b branches -t tags
The --stdlayout option is a nice shortcut if your Subversion repository uses the typical structure:
git svn clone http://svn.example.com/project --stdlayout
Make your git repository ignore everything the subversion repo does:
git svn show-ignore >> .git/info/exclude
You should now be able to see all the Subversion branches on the git side:
git branch -r
Say the name of the branch in Subversion is waldo. On the git side, you'd run
git checkout -b waldo-svn remotes/waldo
The -svn suffix is to avoid warnings of the form
warning: refname 'waldo' is ambiguous. To update the git branch waldo-svn, run
git checkout waldo-svn
git svn rebase
To add a Subversion branch to a trunk-only clone, modify your git repository's .git/config to contain
[svn-remote "svn-mybranch"]
url = http://svn.example.com/project/branches/mybranch
fetch = :refs/remotes/mybranch
You'll need to develop the habit of running
git svn fetch --fetch-all
to update all of what git svn thinks are separate remotes. At this point, you can create and track branches as above. For example, to create a git branch that corresponds to mybranch, run
git checkout -b mybranch-svn remotes/mybranch
For the branches from which you intend to git svn dcommit, keep their histories linear!