You can use a crop or straight stick to keep your thumbs turned upwards. My trainer gives us an equicube when we don't have our thumbs up, it helps a lot
Bend your elbows- If your hands are too low
Use a crop or whip and place under thumbs- If you ride with one hand higher than another
Over exaggerate and flex your wrist out so your finger nails are faced up- If you have piano hands
I was taught to ride with a whip between my two hands! It's hard but gives you solid foundations!
Picture that your holding a tea cup and you can't spill the tea, that how I keep my thumbs on top of the rains and hands off my horses neck :)
Thumbs up! Even though you see most not doing it, it's still very important.
Make sure you are not holding them near your chest as you are pullling it to stop and as well don't hold the reins to high in the air
Low and in front of the saddle. Don't hold your hands like you're riding a bicycle either