Hello Man!
I have a pretty simple way to take control of your dreams to begin and train from there. Just listen to rainy music or water music before going to sleep, it will help your brain to create a sea or a river or whatever with water in it. You will probably fall into it or just force yourself to go in then drown yourself. Most of the time for me it's because i'm trapped under the ice or attacked by some monsters under water, just create your own story or find an ancient dream you remember with this type of expenrience, it's easier for your brain to recreate the dream if you think of it before going to sleep. Then force yourself to breathe under water, just open your mouse a little tiny bit, breathe then you will see you can and you will stop suffocate then breathe deeper and deeper. Your brain will know you're in a dream and you will be able to control from there.
Keep me in touch if you can start to work your way from this!

Mara'