Firstly, the biggest tip I can give to change bad habits is to take a few riding lessons with a good instructor, or even have a more accomplished horsey acquaintance watch you ride a few times. They will be able to see a lot more in person than we can online, even with pics and video, and that will really fast-track your improvement.
Barring that, something that you can do yourself is get a few pictures of yourself riding several different horses and compare them to what you know is correct. Use several pics, to eliminate "odd moments" and pick out issues that are truly poor habits. From there, make a list of what you would most like to change, and work down the list, tweaking as you go. It's really a mind thing - choose a few checkpoints around your arena or trails at which to ask yourself how you're riding. Is your weight in your heels? Are your ears, shoulders, elbows, hips, and heels aligned? Are you asking for every movement with your seat and weight first, and your hands last? Just a few common problems that many riders struggle to break habits with.
You commented specifically on learning how to be lighter with your hands, so I will make a few general comments about that. I just want to point out that that means different things in different disciplines. For example, in western disciplines, light hands on a finished rarely touch the bit. Conversely, a dressage rider must learn to have light hands in contact with the horse's mouth, and light hands equate to educated hands that are steadily there, allowing the horse to seek contact, as well as effectively communicating with the horse about the balance and carriage of his entire body. Although the goals are the same (an educated horse and rider who are working together in harmony with lightness in the aids), the external visual appearance of that lightness is very different in some cases. Just a few things to keep in mind.
One book I can recommend is Sally Swift's Centered Riding. There are some phenomenal exercises and ways to cue yourself into forming good riding habits.