One precaution you must take while presenting is to check if the projector lamp is set to maximum brightness. Usually all projectors have two settings: Standard (or Normal) and Eco. The Eco mode shows dimmer image and saves energy. Make sure you set it to Standard mode for audience size of 10 or above.
While conducting a session at Delhi VAT department, I came across a Sony projector which had THREE settings: High, Standard and Low. Factory setting was Normal. I changed it to HIGH and got brilliant display. There were 60+ attendees – so this brightness boost was most useful.
Moral of the story: Reach early and check the lamp mode settings for EVERY projector you come across.