Need 90degree crown molding hacks please

Make a pattern out of scrap molding for the corners first.

If there's a wrong way to cut molding, I've done it! You may wish to take a few pieces of your mistakes and cut them properly, glue them together and keep that next to the chop saw for reference. A visual always helped me....

https://www.youtube.com/watch?v=9QpnWgGNtOk

https://www.youtube.com/watch?v=lT65t5ANBac

http://www.diynetwork.com/how-to/skills-and-know-how/carpentry-and-woodworking/how-to-install-crown-molding

I found this really helpful https://www.youtube.com/watch?v=g-M-LeBqx_w

Do this for the ceilings.

https://www.hometalk.com/diy/decorate/walls/dress-up-corners-with-handmade-plinth-blocks-13821357?se=fol_new-20180124-2&slg=5381ee30cf3618540028444039b9bf7f-10901811&post_position=1

You can buy corner pieces to match your moldings. Cheap and easy and they look great! Put them up first and slide your long pieces into it.

Thanks everyone. Some great ideas and the videos are so helpful. (Forget how great google can be sometimes). I appreciate y’all. Have a great day!

You can make decorative blocks out of scrap wood and put in corners then you just have straight cuts .You can also buy at Lowes,Homes Depot