It's surprisingly difficult when you think about it. If you're not careful, you leave quite a few plot holes open and you can lose an audience if the barrier for entrance is too great. Oh, you want to get into WandaVision because a friend was talking about it? Well, you have to be familiar with Age of Ultron, Infinity War and EndGame in order to appreciate it. If you're not familiar with them, congratulations on all of the spoilers for those movies. Early Marvel movies were great about being stand-alone with small nods to other movies, but modern ones are getting more and more intertwined and make it harder and harder to be a new fan of. They're following in the footsteps of comics where it's pretty hard to just jump in without a wiki on the side.