There is never going to be agreement about what is essential in a ritual and what is not, any more than there will ever be agreement about what makes a good novel. That doesn't mean there is nothing worth discussing. The steps I have enumerated below are suggestions which were handed down to me, and a lot of insight (not mine) has gone into them; they conform to a Western magical tradition which has not changed in its essentials for thousands of years, and I hand them on to you in the same spirit as I received them.
These are the steps:
1. Open the Circle
2. Open the Gates
3. Invocation to the Powers
4. Statement of Intention and Sacrifice
5. Main Ritual
6. Dismissal of Powers
7. Close the Gates
8. Close the Circle
Suggested free e-books to read:
Anton Szandor Lavey - The Satanic RitualsJarl Fossum - Seth In The Magical Texts
Benjamin Rowe - The Essential Skills Of Magick