I still get nervous, but I've learned to manage it.

Some things that help:

- Keep your changes small. You should be able to fit the entire diff in your head and completely understand the purpose for every changed line. If you can't, split it up.

- Automate the process as much as possible. Invest in learning whatever tool works best for you (Fabric, Rake, Grunt, etc).

- Use a staging environment. This is especially helpful for catching issues like missing dependencies, DB migration problems, etc.