@abdulrahman - Interviews have never been rocket science. There are a few things you need to know: -
1) Understand the industry you are in.
2) Understand the company - read about them widely.
3) Know exactly what they are looking for - why do they want to hire? What are the gaps they are trying to fill?
4) Be clear on what you are bringing to the company - How does the company benefit by hiring you? Carefully map your strengths to their needs.
etc.
The rest are details and/or porojo!
Never count on making a good sale. Have the purchase price be so attractive that even a mediocre sale gives good returns.