My habit is to git pull first (well, actually git fetch and then rebase my local work onto the new head), then update the feeds, then
make -j5 clean download world
(4-core build box) which makes sure that things are tidy, as well as that all the needed sources are available before the compile starts.
You can also use git tag some-name-that-means-something-to-you to mark points in your local copy. Before I started capturing everything with a script, I'd use build-2018-06-14 or the like for my tags.