There are several steps that you can take to prepare for using a projector during your presentation.
First, if it is possible, use a projector when you are practicing your presentation. This will allow you to ensure that the projector is working and that there are no problems opening your presentation on the computer.
Once you have practiced your presentation, check to make sure that what your presenting can be clearly seen from everywhere in the room. Sometimes certain colors are harder to see on the projector display then they are on your computer. Check to see if all parts are clearly visible and change any part that is not. This change could either involve changing the color scheme or adjusting the lighting in the room.
Finally, make yourself aware of the projector being used so that you will know what to do in case there are problems during your presentation. Some basic items that you should be aware of are how to turn it on and off, how to focus the lens, and how to rise and lower displayed image.