If you have just performed a change and you realize you want to immediately do it again, you can hit . instead of retyping it. This is a good way to quickly repeat simple changes.

For instance, if you are adding indentation to a code block with >, you can estimate the number of indents that need to happen and type 3> or you can indent once and then hit . for additional indentation until you reach the right level of indentation.

Check out the docs for more details: :help .