The Sabbats celebrate the larger cycle of the year, and are based on solar events. But witches also celebrate the monthly cycles, and these are based on lunar events. Wiccans very commonly celebrate the full moon (a ritual celebrating the full moon is called an Esbat), and, less commonly, the dark or the new moon. The moon phases also influence what magick is worked at any particular time, as different kinds of energy is associated with different phases of the moon.
It’s easy to understand how the Wheel of the Year affects us, with its influence on seasons, crops, etc. But it can be harder to understand how the energy of the cycles of the Moon affects us. Think about this: the moon affects the ocean, and our bodies are 70% water. Is it too much to expect that the moon would affect us as well? Whatever the cause, the link between the moon and different types of energy, magickal or otherwise, is ancient. It symbolizes the life, death, and rebirth cycle as well, on a smaller scale then the Wheel of the Year.
Each phase of the moon has its own energy, and if you want to work magick, knowing what phase the moon is in and what is the most effective way to work with the energy that is out there and not against it is very helpful.
New Moon: The first two or three days that a new crescent is visible. It is about to begin its journey around the earth. It will take roughly 29.5 days. This is the Goddess as a young Maiden, and thus is a perfect time for magick involving new beginnings (starting a diet, starting a new habit, starting a new course of study). It is also good for magick that involves growth- so it’s a good time to begin that meditation practice, or start that herb garden.
Waxing Moon: From the new crescent to the full moon. This is the Goddess in her Maiden aspect. This is a great time for magick that involves growth and increasing (prosperity, fertility, good health, a new job, etc.).
Full Moon: Ah, what everyone knows witches celebrate. Pull out your cauldron and your wand, because it’s the witching hour. In all seriousness, this is what is known as the Esbat and most Wiccans celebrate it with some kind of ritual. This is the Goddess who is strong in her aspect as the Mother. The energies of the moon are very powerful at this time, and many kinds of magick are worked on the full moon, as well as the Drawing Down the Moon. This is the time for consecrating tools, charging jewelry, working healing magick, working magick to bring things to you- self-love, spiritual growth, financial prosperity, protection, etc. It is also the time to focus on or do magick for spirituality, psychic development, dreams and divination. Each full moon has its own name and correspondences. This website has done an excellent job of laying it all out.
Waning Moon: From the waning gibbous to the waning crescent. This is the Goddess in her aspect as Crone. This is the time to do magick to removing something from your life (bad habits, negative energies, unwanted ties, etc.). This is an excellent time to do a spell to remove barriers from your life. It’s a time for reflection as you benefit from the Goddess’s wisdom as the Crone.
Dark Moon: One to two days before the new moon, when the moon is completely hidden in the sky. This is the time for banishing work, for honoring the Dark Goddess (Hecate, the Morrigan, Nephthys, etc.), and for works of divination, psychic work, dreams, astral projection and dreams. It is also a good time for shadow work, but make sure you are prepared for the force of the energy that can come with doing shadow work at this time. This is a time for rest, relaxation and reflection.
This can seem very detailed, so in general, here’s the rule of thumb; first half of the moon cycle, you’re increasing things; second half, you’re decreasing things.
The question that often comes to mind is “What if an urgent need comes up, and it’s the wrong moon phase?” Well, there are a couple of ways to handle this. One is to just do the work you need to do. The urgency of your own energy will carry you a long way, and this is not some sort of hard and fast rule. The Goddess isn’t going to zap you if you do a banishing spell during the waxing moon.
The other way to handle it is to frame your need in a way that fits with the energy of the current moon phase. If you have an interview for your dream job during the waning gibbous, you could do a spell for all barriers to your success to be removed instead of doing a spell to get that job. Bring joy and inner peace instead of banishing depression during the waxing moon. Most spells can be reworded in a way that allows you to work with the energy of the moon phase and yet still do a spell for what you need. Personally, I feel this is the better way to go if you at all can; that way you’re not swimming against the tide, as it were.