Correct Fundamentals help you "do the right things right".
As a rider, you need to put the fundamentals in place so that the right things happen by habit. Good riders ride well, because their right habits are so ingrained into their philosophy and their thought processes that they do routine things without thinking.
Developing the correct habits is a bit like instilling good manners into children and teaching them to say "please" and "thank you". This can be quite a laborious process to start with. You ask them "What is the magic word?" and the same with thank you and you keep prompting them until it becomes routine.
As an adult, the habit is so formed that to try and not say please or thank you feels very strange. Aim for this feeling in your riding; it should feel strange if you do not do things right.
Now, how do you make sure that doing the right things right becomes so habitual that you do them without even thinking about what you are doing?
From the start, focus on the fundamentals:
Are you aware of what the horse is doing underneath you when you are riding?
Is your style as good as it should be?
Are you restricting your horse?
Are you focusing too much on trying to get your horse into a shape or are you allowing him to go into a shape?
Develop your building blocks of a good seat, then the fundamentals of riding will happen automatically.
My training philosophy is to keep it simple:
Stay in the center of the horse.
Put your weight into your heel.
Have a little kink in your arm.
Create an L shape at your elbow.
Maintain a straight line from your elbow to your horse's mouth.
Maintain an elastic contact that allows you to give and take.
Have a nice open shoulder.
And practise, practise, practise until you can maintain a good position in all paces.
All this may seem like a lot to keep track of, but for those riders who drive a car, you will recognize the similarities. When you started driving, you were bombarded with instructions on a myriad of new things to do simultaneously. Now you do them without even thinking. They are ingrained in you – they are habitual.
Get your correct fundamentals in place, and doing the right things on a horse will be habitual as well.