When buying a projector, there are several factors to consider to ensure you get the right one for your needs. Brightness is a crucial consideration, as it affects the projector's ability to display presentations clearly. Portability is also important, as it allows for easy installation and movement of the projector. Resolution is another key factor, with 4K resolutions becoming more common in modern projectors. Additionally, it's important to research and compare different products before making a purchase, as inflated LED lumen values can be misleading.