Things I Learnt The Hard Way - One Commit Per Change

When working with source control tools, keep one change per commit. Avoid bundling more than one change in a single commit just to "save time".

I've seen my fair share of commits with messages like "Fix issues #1, #2 and #3". This is not something you should do. One commit for fixing issue #1, another for #2 and yet another for #3.

Just note that I said "one commit per change", not "one commit per file". Sometimes, to make a single change, you may need to change more than one file -- it may point that you have a coupling problem, but that's a different issue. You could, for example, make one commit which adds a new field in model without adding a change in the controller to load this field; after all, the controller won't (or, at least, shouldn't) break due the added field, and the model won't break (or, at least, shouldn't) break because the controller is not touching the field¹.

When making a commit, think this: "In case something goes wrong, can I undo this commit without breaking other stuff?" Commit history is stacked, so obviously you'd have to undo the commits on top of that one. And that's alright.

BONUS TIP! If you're using git, you can use git add -p in case you "overchange". It will allow you to pick parts of a file, instead of adding all the changes in the file before committing.