A guide to learning about tunings on the Internet
1. Read Read Read
Not much to say in general since you are already on the xenharmonic wiki. There's a lot of math out there related to tunings; it's up to you how deep you want to go into it. Just keep clicking links!
1a Remain Skeptical
A critical element to your approach to learning about tunings in the internet is skepticism. The internet has a tendency to allow misinformation to prevail so, especially in this niche of relatively new theory, be sure to keep in mind what interest is advanced by someone else's writings, and what it is they may be leaving out.
1b Tools, not Rules
Regardless of the objective veracity of someone else's claims, they usually provide (and are often motivated by) some new or different approach to music making. If one approach is musically useful to you, feel free to use it, and if it is not, feel free not to, regardless of how many other people say it is the "right way".
2. Listen and Play
It's easy to spend a disproportionate amount of time on #1, but two of the best ways to learn about xenharmonics are to listen to and to play them yourself. Check out the MicrotonalListeningList for the former, and the Software and Instruments page for the latter. Most of these scales and tunings are brand new, so it's almost a given that you'll learn things that no one else has figured out by playing and writing yourself. That means you won't read about it anywhere until you write it yourself!
Naturally, some find it encouraging to interact with others working in the same area of study. Here are a few relevant online communities: