When I first started (and why do so many of my thoughts start out this way....makes me feel old!), the degree system and the whole year and a day thing was huge. Every book mentioned it, and I know a lot of the people I was learning with (we were all solitary and learning from books and whatever other sources from the internet we could get our hands on) felt that practicing for a year and a day was more or less required if you wanted to consider yourself a witch.
The word used then was dedicant. For that first year (and a day!) you weren't considered a practitioner, you were learning. And the thought was that it would take you that long to learn enough to make an educated decision about whether or not this was something you wanted to continue to pursue or not.
I think this decision making process has a lot of value. Firstly, it gave you a body of knowledge that related to the path you were wanting to take. This core information was the foundation on which further practice was built. But it really did serve to give you an idea about the things you would learn about and do in the future. If it didn't work for you in the dedicant period, if you weren't feeling it or if you just couldn't shake the idea you should be doing something else, then it probably wasn't for you.
I think it gave people a graceful period of time, especially when working with a new group, where they could say that they had given it an honest go, but that it just wasn't right for them. It also gave you a grace period, where you were still a dedicant, and therefor weren't expected to know things. I think that offered a lot of peace of mind to people. They were still learning, and everyone who knew that understood that.
Most systems had their own list of things you should know by the end of your year and a day. And by know, they meant 'be familiar with the basic structure and comfortable doing the actions required', not that you should have mastered it. While many systems had differences, there were some things that were common to almost all. Things like: casting a circle, knowing the Sabbats, some form of divination, elemental correspondences, working with candles, working with incense, deity knowledge, grounding and centering, shielding.
I rarely see the year and a day thing mentioned anymore. Most 101 books still include the basic information, but it's just labeled beginner now. The term dedicant has fallen out of use, and that is understandable, because it was most commonly used to refer to people joining a particular group, and many of the 101 books now assume you are going to be solitary (or at least not joining a specific group if you are learning from a book).
But I think that the idea of spending a year (or more) and really buckling down the basics has a lot of value. Where I think it can really shine is if you were to spend that year figuring out what you thought the core practices were for you.
If you look at the year and day as an outline for future practice, you will have a framework for the the type of practices you will do throughout your year. Many of us celebrate a yearly cycle of holidays, whether it is the eight Sabbats or some other set of holidays that have meaning for you. Though this cycle may evolve as your practice does, having a starting point of times throughout a calendar year that you wish to honor helps give you landmarks throughout the year.
From there, you can examine other cycles you might wish to honor. Many people honor the cycles of the moon and sun. I was introduced to the idea of Esbats as meetings of a coven once a month, but I have also heard them referred to as rituals to honor the moon cycle. These smaller cycles can give a lot of structure to a regular practice, but some people find them too restrictive.
Typically, for rituals like the ones mentioned above, a circle is cast and a more formal ritual structure is used. Figuring out what your ritual structure will be is a necessary step in building a practice. I started out using a much more formal ritual structure than I use for most rituals today. Even though I don't use the same structure now, I definitely think that working with the more formal structure has influenced my practice and I am glad that I started out with something more formal. For some people, working the other way is better, and they start out with a very simple ritual structure and then build it up as their practice evolves. Whichever way you feel comfortable with, explore a couple of different types of rituals and then practice with the one you find most appealing.
I think an important thing that is often overlooked in a lot of 101 books today is why we do the things we do. Spending time researching and thinking about the things you add to your practice makes it something that is a part of you instead of just something that you do. I found it really helpful to put my thoughts on paper, as if I were writing up a topic for a school project. I also found that discussing things with others helps me a lot. Whatever way you find works for you, really put some thought into why you like and choose to continue doing the things you do.
Ethics are something that also seem to fall by the wayside. There are a lot of ethical catch phrases out there, like “harm none” and the “threefold law”. Knowing what you find acceptable and unacceptable is very important. If you don't think about it ahead of time, you may find yourself in situations that you aren't prepared for. It is much easier to do things that you aren't really comfortable with if you haven't spent time figuring out what you think is okay. There are lots to consider when it comes to ethics.
Do you think it is okay to take money for practicing on someone else's behalf? What about teaching? Is it okay to use magic on someone without their permission? What about healing? Is eating meat a problem for you? How important is green living? These are just a few topics that many people feel very strongly about, and sorting out how you feel about them gives you a starting point for figuring out how to live your life in a way that makes you happy on all levels.
One final thought about the year and a day. Learning is it's own cycle, and every year we have the opportunity to continue to grow and develop our practice. My own practice changes every year as I learn new things, meet new people who inspire me, and find new ways of thinking about the world. My core practice changes as well. I am constantly looking at what I do and seeing if it is the best thing for me. I am very much someone who both clings and changes. I will hold a practice tightly to me, for years and years, but the moment it stops working I will search for a new way of doing things until I find something that fits. I can walk away from things I have done for decades without looking back. And sometimes I do cycle back around and pick up old practices. Everything changes, and trying to hold onto something just because it is how you have always done things can mean you are stifling your own practice.