Ian Jones has written an incredibly comprehensive guide to contributing to WordPress core on the Delicious Brains blog. They’ve really been doubling down on good dev-centric content lately, which I love to see.
The post includes a focus on an area that doesn’t get enough attention, which is ticket workflow. There are specific landing pages in Trac to see tickets that are good for first patches, need unit tests, and other workflows that make it easier to get around and find a place to get involved.
It may be intimidating at first read, but once you get through your first couple of attempted patches, it gets easier and starts to make sense. Also, a lot of WordCamps have contributor days now, and that’s a great opportunity to sit next to someone that’s done it dozens of times and learn from them.