Last year when I was practicing weightlifting I worked a lot on improving my posture since I always had the classic shoulders rounded forward+ winged scapulae posture. It has improved tremendously, but I feel like in some of F1's exercises it still affects me. Precisely I'm referring to the two exercises listed in the title. After graduating from PPP I've decided to come back working on those after I reanalyzed a video of myself performing the exercise (incorrectly). Do you have some tips on keeping your shoulder blades in the right position during the whole movement?
Regarding single arm planks I just need a confirm that what I can do is actually acceptable as mastery form. Here are two pictures to help you understand my situation. Thanks for your time 
