As a back end dev, how can I make life easier for the front end devs?

I would say that working closely together with the front-end devs is key. Listen to what they are trying to do, and see where you can help. Mind you though, that it should be balanced, because you want to avoid doing work that is unnecessarily complicated to make the life of the front-enders better.

If you are planning to have a REST API. The single best thing you can do is to setup automated API documentation.

Checkout https://dredd.readthedocs.io/en/latest/

- Automation. Automate builds, blue/green deploys, automate building and provisioning the feature branches so they can be tested and quality controlled.

- Document everything not automated.

- Create version matrixes that are automatically updated and easily available (JSON, YML, Markdown)