I used to have the same problem with my hands and arms, then my instructor gave me 2 pieces of key advice that, once id frogging mastered (im a slow learner and quite whiney im told
) it made all the difference.
First of all, pretend like you have an egg under each elbow, you have to hold the egg without either squashing it or dropping it. This will bring your arms out from your side so that you have the correct arm carrage. You don't want your arms to be squashed in at your sides, or poking out like wings! By doing this tecnique you will soon develop a nice soft elbow that's fluid.
Second of all, and this is easy peasy when you mastered it. Pretend you are holding a cup of liquid gold in each hand, the top of the cups should be level with your belly button. If you drop your elbow or relax and open your fingers the cups will tip forward and you will lose your precious load. If you bring your elbow up to much or clench your fingers the cups will tip backwards and you will have said liquid gold dumped all over your saddle...not a good look!
I know these are basic childs methods, but seriosly give them a go, youll be suprised at how well they work!