GitBestPractices

For a nice, relatively brief overview of Git's basic usage, please see the Pro Git book by Scott Chacon, available for free online. If you want to understand the nitty-gritty, check out Git From the Bottom Up. There's also a fantastic blog post at Github entitled How to undo almost anything in Git -- this is required reading.

Otherwise, here are a list of typical "dos" and "don'ts" for Git, some with a specific eye towards Open MPI:

Do

make smaller, logically self-contained commits
write nice commit messages, with a concise subject line and a useful description of what change is being made and why
(In general) Rebase your local work before pushing up to ompi/master instead of creating merge commits that say "Merge branch 'master' of 'ssh://...'". Unfortunately, the default behavior of git pull is to merge instead of rebase, see here for how to change that default.
If you think you screwed up a repository (yours or a shared one), STOP.
- See this Awesome flow chart on how to get out of Git messes
- See the "How to undo almost anything in Git" blog post at Github
- Ask for help on devel@open-mpi.org. Many Git operations are reversible if you don't take too many steps in the wrong direction.
run git gc on your repository periodically, it will speed up many operations and shrink the space consumed on disk by your .git directory

change published history
change published history!
CHANGE PUBLISHED HISTORY!!
push non-master branches to the main ompi repo
push non-master branches to the main ompi repo!
push with --force or --mirror to the main ompi repo
delete or rename published tags -- this is a real pain to unwind
make large rambling commits that intermix multiple unrelated changes
make unnecessary whitespace changes in the same commit where you are changing logic
commit any large binaries to the repository, this will rapidly increase the storage space required for everybody's clones
use git filter-branch unless you really know what you are doing, and especially don't use it on published history
use git pull instead of git pull --rebase for normal local work that will be pushed up to ompi/master (see "Do" above