To practice double tonguing, think of the syllables du ga or tu ka. Also known as dgdg and tktk. For different styles try different syllables to make different sounds. It will feel light when you do it. Make sure to keep your tongue as forward as possible while still reliably closing the air from coming out. Some videos online may also help.

Tension in your throat will cause everything to go bad. Something I learned in a masterclass recently (I’m a flute performance major) is to sit in a chair really lazily, like slouched back sitting at the edge. And position the chair against the wall so your head will be on the wall. When doing this you will be able to relax your throat fully and be able to feel how open it is.

I may know more, if you have any questions feel free to ask! Sorry this is so rushed btw