There are 3 ways you can install your projection screen. The right way depends on your room, so there's no universal best way.
Here are the 3 ways to hang up your screen with the advantages of each method
1. Wall mounting
The big benefit from hanging a screen up on the wall is that you can decide at which height it will be. By hanging the screen lower or higher, you can determine at which height the image will start. This is especially handy when your screen has a small or non-adjustable top black border.
The disadvantage of this method of installation is that the case of the projection screen is clearly in sight. So it's not ideal if you want an "invisible installation".
2. Ceiling mounting
When you do want your screen to be virtually invisible, it's best to install it close to the ceiling. With the screen that high up, it is not as much in sight. But, you lose the flexibility to influence the starting position of the projected image. So it's best to use this installation method when your top black border is large and can be adjusted.
3. Suspended installation
If you have a sloped ceiling or you want to create the effect of a floating screen, you can use wires to suspend the screen from the ceiling. It looks great when thin wires are uses, as the floating effect is something you do not see every day.
Having the screen hanging from wires does affect the stability. You notice this most when you operate the screen (especially when you have a manual screen) or when there's a draft in the room. That means it's only suitable when you know how to operate the screen carefully.
It's not an easy installation either, because to get the screen level and balanced can be quite a bit of work. The exact amount of work depends on the design of the case.
Conclusion
There are several ways to install your projection screen. Wall mount the screen when you do not have a flexible or large top black border. Fix it to the ceiling if you want the case of the screen to be less visible when not in use. When you have a sloped ceiling or you want to create a cool looking installation, you can not beat a suspended projection screen.