I don't feel like explaining these here. I recommend reading any basic Wicca book to find out about these things. I don't think I'd be able to tell you anything they won't. I do have a few comments to interject. Many books focus on the material aspects of ritual preparation, yet I think that it's more important to mentally prepare than to physically prepare. So don't neglect your state of mind, you should have a feeling of readiness and competence, and a knowledge of exactly what you intend to do. This is not to say that you have to have a ridged plan prepared for your ritual. By all means, improvise. But know your intent. Know what you DO want to include and what you DON'T want. Use as much or as little structure as you want. Even if you have something specific planned, be open to the possibility of changing that on a whim, because sometimes plans don't work out. Some times things catch on fire that you didn't realize were flammable and you have to change how you're going to offer burnt herbs to the Goddess (sea shells crack at amazingly low temperatures, btw). Speaking of flammable, don't worry if something silly goes wrong. If you accidentally call on the Great Hairy God instead of the Great Horned God, no worries. The deities have a sense of humor. Also, if things just keep going wrong during a spell or a ritual, try to take a hint.
In a lot of books I've read the elements are located in the following directions.
N- Earth, E- Air, S- Fire, W- Water
I do it differently. While surfing the web one day I found a page called RE-THINKING THE WATCHTOWERS or 13 Reasons Air Should Be In The North by Mike Nichols arguing for aligning the directions this way. I strongly recommend reading it. It was such a good argument, I decided it was right, and went with it.
N- Air, E- Earth, S- Fire, W- Water
Many elemental invocations begin in the north, but I begin mine in the east (keeping to the idea of beginning with Earth).
