Open the garage door all the way and wipe down the tracks with a dampened cloth. If dirt and debris has gotten trapped in the track, it will stall the garage door as it descends.
Climb up on a stepladder and find the force knob on the back of the garage door opener’s motor casing. Turn up the force setting slightly and see whether that causes the door to stop sticking at the mid-point. A force adjustment is often necessary if the weather turns and the materials used in the door swell or shrink.
Check the metal rails to ensure that they are not bent. If the rails are bent slightly, pull them back to true using a pair of locking pliers. If the rails are bent significantly, you might need to replace them.