As a trainer I cannot help but stress how vital and important lateral work is with your horse. It is the foundation and building blocks to training a truly soft horse. A horse that is soft and giving laterally will be far better off than a horse that bends vertically.
Make it a goal that your horse is soft equally to each rein at the beginning of your ride. He should be able to flex without feeling the need to move his feet. Your goal also is to have level ears. If the opposite ear is lower then he is not truly bending behind his ears at his poll, rather he is only giving his jaw!
Lateral work is the key to fixing many common problems!