One of the most important ways to be able to play more difficult works is to get your arm and wrist to relax and not to be stiff
Try when you first sit down at the piano, play Just C-D-E-F-G-F-G-E-D and repeat. Do it very slowly, and first hit C, Don't think about going to the next note yet; make sure you're wrist and arm are very relaxed, then move on to D, and do this also when you play scales. And when you push the notes down, just use your fingers, try not to push with you're arms, but later you will need to use the weight of your arms to get more forte and more tone.