Hi Enriana, I'll try to answer your questions:
Do you keep a lot of spreads in your head, or do you refer to an outside source (notebook, website, spreadsheet, etc)?
There are some I already remember because I keep using them such as the Celtic cross and I sometimes put some innovations. Most of the spreads I use i also get from our AT forum as well as books. The AT is quite extensive and varied so I am often able to find what I need but just put some variations.
Do you have a bunch of general spreads that you tailor to a situation, or a few spreads for each general category (relationships, work, self-exploration, etc) that you pick and choose from?
In my case, the spreads depend on the questions or issues I raise. There are moments wherein I use a particular spread but change some of the position meanings. Often, I create my own spreads when i discover new insights.
Do you have a specific "go-to" spread, or do you try to use as many different spreads as possible?
The Celtic cross with variations is a favorite. I also discovered the Be Inspired by the Muses spread from here as well as the Colors of the Rainbow which I consider as favorites. I Use the celtic cross for general readings to know where I am right now and what I should focus on in the next few weeks. The Colors of the Rainbow which I picked up from here is what I use for understanding changes or issues and how to deal with them or what to consider. If I want strength and just to feel whole, I use the Muses. I don't limit myself to these but I find them quite interesting.
Do you prefer to stick with spreads you already know super well, or do you like to learn/try as many new ones as you can?
I'd like to try as many as I could which is why I often pick up some of these from AT.
I do keep a journal of the spreads I use.
I hope this helps.
