You may find that you can co-ordinate your time at the yard with someone else if you ask around a little.
You can use some of the basic dressage tests to give you schooling ideas, they look very simple but are hard to do well. Each movement is simple to perform but ride them in different places around the school not just from the regular markers & work off the track away from the support of the 'wall', linking them together smoothly & using lateral work can be more tricky - this will give you an idea where you & your pony would benefit on working. Not all exercises have to be done as per the 'tests', on the flat however you can incorporate jumps & using ground poles can be challenging too. Maybe you could have a regular lesson from a freelance instructor - ideally once a week - this will give you some 'homework' ideas to practice or watch someone else's lesson. Or try to share a lesson with someone or visit clinics or competitions. Just trying to ride to your favourite music can be fun - working on your balance, rhythm & form through transitions & school movements - maybe making up your own routine? Don't forget that you need to spend 10 mins on your warm up & at least the same on coolong down after.Hope this helps.