I am fascinated by Calendars, which I find slightly ironic because I am horrible with time. Seriously, it is not uncommon for me to forget which day of the week it is (and there is no way I can tell you the actual date without looking at a calendar, computer or my phone). But I love the structure of a calendar, the fact that it comes with all kinds of partitions and ways to organize. I love patterns, making patterns and exploring them!
There are a ton of calendars that can be applied to my practice. To start at the most basic, there is the Wheel of the Year. When I started learning that was a huge part of pretty much every Pagan and Witchcraft book. I still have to pause a moment now when people tell me they don't follow the Wheel. I am fine with it, really I am, but the Wheel is one of the pivots of my own practice, so I have to step outside myself and remember that my path isn't everyone's path.
One of the things I love about the Wheel is that it is a never-ending cycle. The Wheel turns, and comes around to where you started (and you can start anywhere on the Wheel!) and then keeps turning. One of my first calendar creating experiments was to make a circular Wheel calendar. I'm a pretty visual person, so having a list of 8 days to remember just wasn't working for me. I drew out my circle, marked the spokes, and started filling in different attributes and what not. It made it a lot easier for me to not only really place each of the days on the yearly seasonal cycle, but to see the interaction between the days.
After the Wheel of the Year, I think the lunar cycle is the next most common way of marking time. There are a lot of spells and rituals that suggest being done at a particular phase of the moon. Many practices are repeated on a particular phase over several cycles of the moon. It used to be said that covens would meet on Full moons for regular Esbats (which is not something I see as much talk of now). What I find wonderful about the cycle of the moon is that it is a fairly short cycle. You can work through an entire cycle in just under a month, so it is a good starting point for a lot of things.
In the last couple of years, the names for each of the full moons has become very popular, and while I did encounter a lovely progression of moons over a decade ago, they have become more readily available too. What I love about the progression (marking each full moon in it's place in the year, and not just seeing each full moon as a 'full moon' and nothing more), is that it echoes the Wheel cycle, but often with a different focus. Generally I see the Wheel as focusing on more of a grand, outward scale, while the moon progression is more inward and personal.
I took French as my language in school, and so was pretty familiar with the days of the week being named after planets, and it was pretty early on that I learned the deities that the English days of the week are associated with. Having Norse leanings, it fits quite well with my personal inclinations. Again, like the cycle of the moon, the weekly cycle gives you a very short cycle of different energies to work with. I think it is a great way to start thinking about how to approach problems from different angles. So if it is a Friday (generally associated with love: Venus and Freyja/Frigga), but you were having conflicts with a co-worker, you might tailor your working to harness that more gentle energy and work towards peace as opposed to creating more conflict.
Even within a day, there is the cycle of morning, noon, evening and night. Everyone has their own awareness of the energy of a day and how it changes. I am a night person, so for me, mornings aren't full of energy (or at least not full of energy that resonates well with me), so I have to adjust my own self so that I start my day in a way that lets me be functional (and not just want to crawl back into bed!). Likewise, I have to make extra sure that at night I am winding down, and not winding up.
I know some systems break it down even further, with correspondences for every hour of the day, but I find that to be just too much. I have at least one chart like that written down (because I love charts, symbols and Named things, and this chart had it all), but never used it.
I should also mention there are a lot of cycles that revolve around astrology. Astrology is one of those things that I find interesting, but really haven't studied enough to be fluent in it. One of the calendars I check every day shows prevalent astrological features, but beyond noting them, I really haven't done that much work with them. Most people know at least one of their astrological signs, even those who aren't in any way, shape or form Pagan.
But back to calendars and my practice. With all these different systems, it can be pretty confusing to get it all sorted out into one working system. I actually tried to make a working calendar that tracked the moon progression, moon cycle and wheel of the year. It involved rings that could rotate behind a front plate with slots cut out (so you would only see the current place on each cycle). It was kind of unwieldy, and to me, it lost some of it's impact because I couldn't see the connections as easily.
I still haven't figured out the best way to do a working calendar for my personal practice. What I do know is that I will keep working on it. I want to be able to (easily) track the days that are important to me and my practice. As my practice has progressed, more days have been come important. Some have phased out (I have several “Book of Days” type of books/websites that list all kinds of festivals or days, and some that seemed very interesting at the start of my path no longer appeal to me). I think that keeping the calendar vital is very important. To me, even something like the wheel of the year, which has been a part of my practice for pushing two decades, is new again each year as I add more knowledge and the meaning for me changes.