Hi!
First and foremost, if you haven't had a look at the Guix manual yet, I recommend starting with that; this is usually my first stop when I'm working on anything Guix-related and come across something I'm not sure how to do. For packaging in particular, I would start with the package reference section.
Perhaps you might find example-oriented resources helpful, too. Here are some links that I included in my notes as helpful guides during my first time making a package definition:
- https://jyscao.xyz/guix-packaging.html
- https://guix.gnu.org/en/blog/2018/a-packaging-tutorial-for-guix/
- https://guix.gnu.org/en/cookbook/en/html_node/
In addition to the above, consider browsing the Guix repository which hosts a practically infinite store of examples for you to sift through and learn from.
Depending on what you're packaging, you might also find it useful to look at the Nixpkgs equivalent (if it exists) which you can draw some similarities to. I don't often do this though and sometimes it can make things more confusing since it's not always a 1-1 match, but I want to put it on the table nevertheless.
Lastly - there might be times you'll encounter confusing errors or maybe you have a question that the above resources can't really help with: I highly recommend searching through the Guix IRC channel archive (or joining it!). The more experienced bunch of Guix users (and developers too) can often be found there sharing their great wisdoms. I frequent the logs often, which have been so immensely helpful to me that I wrote a script to scrape the archive so I can search through them more easily with grep.