Say you have 12 commits on a few files for a branch that has not been reviewed yet
Here is a way to make it look like a better, cleaner story:
$ git rebase -i HEAD~12 #number of commits you have on your branch
# In editor window, replace all `pick` options for commits with `squash` or `s`
# Hit escape and write `:wq` and hit enter
git reset HEAD^ # will unstage all files you have in one commit
git add filename
git commit -m message
git add filename
git commit -m message
...
git push -f #you need to force-push as branch was rebased, history is rewritten