Neptune is the eighth planet from the sun right behind Uranus (tehehehe). Neptune has 5 rings with 14 moons. Because of the color, it is named after the Roman sea god Neptune. This gas giant takes 165 years to orbit the sun lasting in one sign for about 14 years depending if it is going direct, or if it is going through the various stages of retrograde.
Neptune rules the 12th house, co-rules the sign Pisces with Jupiter even when Pisces is the sole expression of Neptune. With water as the element for this planet, with a mutable modality. Even though the god Neptune is male the planet is feminine given that the sign, house, and element attributed to it are all feminine Neptune is about illusions, glamour, it is elusive and cunning. Keep that in mind when you are dealing with Pisces most of the time the victim card is a cunning ploy. Very few Neptunian/Pisces/12th house people are truly gullible. If they listen to their intuituion they realize any games someone else is trying to play with them. Often times the seasoned Neptunian is five steps ahead. Do not underestimate them.
Neptune is a planet that governs the contemporary in a sense it is a generational planet like the rest of the modern planets Uranus and Pluto included. It regulates over the collective subconscious, and it is a planet closely related to the other side of the vail and the dead. Yes, I know it is more recognized that Pluto rules the dead. Though from experience, personal and professional, Neptune dominate people or those with strong 12th house placement and Neptune aspects encounter more of the other side than not. The difference in encounters of death between the two planets is from perspective. Neptune accepts death and the dead as natural and every day whereas Plutonic death is a catalyst for transformation. With Pluto, it is felt more harshly than not forcing the softer side of someone to have a mini death within in order to continue on. An example of Neptune dealing with the dead someone with Neptune in the 4th house may grow up near or across from cemeteries and are more inclined to have a mother or family who can see the other side. Whereas a Plutonic 4th house person would have to go through power struggles, violence, and symbolic death to survive their ordeals. When death happens Plutonically it is soul crushing. Though, think of it as something to make you durable.
Neptune dominant people are imaginative, creative, most of the time they are a bit psychic. They are very artistic, also can easily pick up makeup and glamour better than any other planetary dominant. They need their time alone to recharge and space to. There may be a tendency to desire to get lost through spirituality or substance abuse.
The opposing planet for Neptune is Mercury. The Neptune Mercury dynamic is of vagueness and precision respectively. Though both planets are about understanding the ever-changing world around them Neptune does so by recognizing the subconscious and emotions that are by nature incomprehensible. While Mercury gains understanding in its environment deducing topics outside of emotions in practical ways. For the feminine expression of Mercury what makes sense before should make sense again. Neptune moto would be what is is or what will be will be. Then flip a situation to benefit the Neptunian.
If you want to work with this planet metaphysically or magically, I would advise studying the ocean, learning about ocean deities. Study the gods Poseidon, Neptune, and Yemaya, learn sailor lore. a good day for Neptune is Friday just as it is for Venus. Learn about all forms of art, music, art, theater, etc. Understand the subconscious and metaphysics. I hope you the best on your journey.