This horse has a too-low headset, and is behind the vertical in almost every photo. He is not tracking up at the trot and his back is sunken in. He is not taking up any contact with the bit. He has really nice conformation [Good shoulder, uphill build!!], but his muscling is poor due to the way he is being ridden. If you want to ride true western pleasure, this is not the horse to do it with!
First off, encourage him to move forward with purpose. He needs to have his back hoof fall into the print the front hoof made when he is trotting--this helps engage the back. As you push him forward, do NOT hold contact with his mouth. [Also, take off the flash noseband.]. You need to let his energy come UP and OUT, not down and backwards as it is doing in the photos. Correct contact is taken when the HORSE takes up the slack in the reins--not when you grip them tighter. Until he wants to take the bit and create contact, you want a really light, following contact and encourage him to be relaxed at the jaw, but with his neck up.
This horse will do beautiful long and low for you once he is muscled up to do so--and this will build up his non-existent topline. He is very angular and his muscling shows inconsistent, incorrect work.
It kind of sounds daunting, but I've done it too. Here's my TB when I first got him, in five days a week of INCORRECT work:
Very angular. Note this horse was not thin, just angular.
Here he is, several years later, with MUCH less feed, only three or four days of work, but it actually being correct:
I show these two pictures often because people often say 'oh my horse is just lean!' when really, the muscling is just incorrect.
Here is a good picture to show you what correct contact looks like, also with this horse:
His head is in front of the vertical, his poll is the highest point, you can not see a break in his neck behind the poll (which indicates a 'break' in the flow of energy!), and he is tracking up and lifting his back. Your horse here reminds me of mine--a lot of potential, just needs the right tools!
Just let me know if you would like me to elaborate on anything.