I've just started looking at Pebble development. For me, battery life is key, and 18 hours for Apple Watch just isn't enough. I've just upgrade to a Pebble Time, and decided to have a look at development.

I'm not going to post a tutorial, as the ones on the Pebble site are so good.  Here's a quick overview:

Apps are coded in C.  This takes a few moments to get used to!  I think there is a JS option too.

The Cloud Pebble IDE (https://cloudpebble.net/ide/) is brilliant! It included everything you need, including an emulator! Uploading to a real watch for testing is easy too.

The tutorials are really well written.  Start with this one https://developer.getpebble.com/tutorials/beginner/hello-pebble/