Personal training is not only for weight loss / muscle gain, but also should functional movement be focused on. Some mobility exercises to start your training is not a bad idea.
Try some from your next training.
Wall glide
Why thoracic spine mobility?
when you want to reach out something high and thoracic spine doesn’t move as much as it should, the next part of the body has to compensates which is lumbar spine. Therefore, you wouldn’t be able to keep your neutral spine.
start 
end
Start from your torso flat on the ground and arms bending, then slide up.
Some people may feel in pain while sliding up, then go as far as the point you don’t feel in pain. Don’t force it. This is not one day fix thing.
The deviation of wall glide
You want to maintain a torso on the ground all the time.
Open book
Wall glide works on “Y and Z axis” (I wish it would be as easy as CSS transformation lol), now we need to work on X axis.
Open book is the perfect for thoracic spine horizontal movement.
start 
end
As the name says, you will open your arm to the other side.
Here are couple things to make sure
Knee position
A knee has to be attached to the form roller all the time. As you start, you want to push the knee down. That way, lumbar spine is fixed and movement will come from thoracic spine.
No momentum
Any kind of stretch should be performed with controlled tempo. Ballistic movement is only harmful for your body.
Click here to see the part 1