This is the biggest thing you can do to use your projector outside during the day. If there is any way you can set up something to block out at least some of the sun this will make a dramatic difference in viewability.
If you are outside, it can be tough to block out all sun but using a tent canopy above your projector can help block out some light and give you a better viewing experience.
If you lack a canopy tent, then you can always try and position your projector, and screen away from any direct sunlight, and try and watch your movies in the mid-afternoon when the sun isn’t too bright.
Conclusion
In the end, there are a few ways to make watching a movie from a projector in the day a little more enjoyable. The main issue is the brightness of the sun, which you can do little to nothing to change which can get frustrating. I would say getting a grey screen, and changing the settings on your projector will be the cheapest options and have the largest effect.
In the end, it might be more worth it to watch it a little later in the day with less sunlight, or just going inside and watching it with your curtains drawn. Unless you can find a way to block out the sun you may be fighting a losing battle, unfortunately. But, don’t get down as spending time with your family/friends outside even if you can barely see the projection will be a great time!