I'm looking to gather information on etiquette and best practices (hell, even an introduction) on how to use Git hub properly. I recently signed up to post a comment about a bug in an R package and I'm just looking for any tips.
Other than that there really isn't a defined "etiquette" as it's really just dealing with developers directly (most of the time - unless you're reporting stuff for a big package that has a team behind it). If you have a specific question I'd be glad to provide some insight but really just poke around for a while.
It sounds like you just want to raise an issue on a particular repositories page though. If you're the one initiating the issue it's nice to also provide the output of sessionInfo() and possibly Sys.info() after you've encountered the bug so that it's easier for them to spot any obvious issues with the installation (maybe you're using an old version of the package or an older version of R or something like that). It's also good to provide the code you ran, the output you got, and the expected output with some comments on why you think your output is wrong. Basically just provide as much relevant info as possible to avoid a lengthy back and forth.