Remove seats in the front area
The area between the doors is often occupied by people standing, while the seats in the back are empty.
Obviously, people gain more from standing there than from sitting in the back. If this is a city bus, with short distances between stops, people might value ease of getting off the bus above sitting. When transitioning from a walking / standing position to a sitting one, you often must rearrange your luggage, like a backpack. If you’re only on for a few stops, you may not want to bother.
Also, in the area between the doors, people have access to two doors, which enables them to pick the other if one is blocked or out of reach.
By removing the seats on the left, the right, or even on both sides in the area between the doors, you create more room for people to stand, increasing the capacity of the bus, and making it clear that you can sit in the rear, or stand in the front.
This separates two different groups of passengers: those only on for a couple of stops, and those on for a longer ride.
It would be best to have a couple of seats directly behind the driver, designated for people having difficulty walking. You don’t want them to have to make their way to the back of the bus.