Git

Some rules of thumb:

• Don’t use git add .. It will probably bite you into adding to much stuff – creating commits exaclty with what you want is a better habit to get.

• Don’t use git pull to retrieve the content of shared branches. A typical example is to commit on a branch, try to push it to GitHub, which refuse the push because it is not a fast-forward one. If you simply pull, you’ll create a merge commit, which is probably not needed.
  Instead, use something like git fetch and rebase. You can also use git pull --ff-only to “tentatively” pull, i.e. fail if it is not a fast forward (in that case the remote tracking branch is already updated locally).

• Before creating a new commit, use git status and git diff to decide what to commit. Adding a -v flag to git commit is also an option to review what you are committing.

• Before pushing a set of commits to GitHub, use git log and its variants (e.g. -p or --graph) to review what you will share.

Some rules above could be rephrased as: use commands that have the precise result you want (instead of commands with multiple kinds of results). Or: double check that what you want to persist in the history, and share with others, are really what you wanted.