Well I used to be an eventer and didn’t start straight dressage till after my accident in 2013. This is what really started my para career I guess.
My advice to beginner dressage riders, or any riders for that matter, is to ask for help! The more assistance and particularly coaching you can get the quicker you will progress. My other advice would be that the harder you work, the greater the results you will see! So put in the hard yards, go above and beyond and you will achieve your goals!