try to build it in as many way as possible changing the configure flags
run each build against some testcases [maybe try to automate it if possible]
Double check documentation, manpages and doxy, grammar mistakes won't make the code fail but look bad.
prepare the release documents
NEWS : should contain a synthetic summary of the changes, git-shortlog may help a lot
ChangeLog : should contain a relatively list of the changes, git log with the right format string can do that for us, if there is time delete the less meaningful commits
RELEASE : write a short essay on what we did and why people should use the new revision. Mention of known issue should be done there.
tag the release
use git-tag -s -m “Release $version” v$version
prepare the tarball
$ git archive --format=tar --prefix=$app-$version/ v$version | (cd /var/tmp/ && tar xf -)
$ cd /var/tmp/$app-$version
$ ./autogen.sh
$ doxygen
$ cd ..
$ tar -jcf $app-$version.tar.bz2 $app-$version
put it on the website updating the pages and preparing a release newsitem.