Cutee horse! I don't see too many flaws, but I think your legs should be back a bit more. To help this, you can open your calf & stretch your leg down & back (so it is like a line from your shoulder to your heel). ;) You are also leaning forward a teeny bit, try to sit back (to help this, relax & breathe), not too far back, but a little bit. Overall you look good!
I think nadia means that the pony is on the forehand :)
You are leaning too much forward and it looks like you could drop your stirrups a hole or so. This will help bring your leg down into a nicer position and once you sit up a little more that will being your shoulder, hip and heel into line.
If you get yourself in a better position you will be able to start working on getting his head down and get a nice frame.
As said, thumbs up :) you should be pointing your fist at the bit :)
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.