you dontlook to bad but I would suggest to bring your lower leg back a wee bit as others have mentioned, creating a straight line from hip to heel. This will help in sitting more squarly on your seat bones in the saddle. In a few pics you are leaning forward. roll your shoulders back keeping shoulders inline with with hip ( Shoulder in line with hip, hip inline with heel, heels down toes up). As for your hands yes you want tumbs up , keeping your elbows in, this creates a straight line from bit to elbow as your rein does not end in your hand, you should want to work from the elbow, eliminating "broken wrists" and "puppy dog hands". For your heels yes they are down but it looks like you are trying to force them rather then letting your weight sink threw your body into your heel and lifting straight up at your post by using your ankle. Remember keep your eyes up looking forward to where you want your horse to go. If your eyes drop, your head does, shoulders drop and the rest will follow throwing your body out of line.