Dressage is dressage, stadium is stadium and if you are considering an event you should be able to do those. The unique part of eventing is the cross country - and that is the thing to practice before the event. Cross country riding is all about rhythm, balance and line. You set up a rhymical canter in a good balance, that takes account of the variable terrain and the line of your approach to the jump, and you use your balance to control speed, and then allow the horse to jump out of its stride. Cross country means a partnership where you sort out rhythm, balance and line and then trust your horse to sort out the jump. Micro-management doesnât work well in xc. The horse should be jumping more freely anf forward than in the stadium. This essay is why I am suggesting you get as much practice xc as you can manage, with a good trainer, before you take on your first competion.
Go and school XC with an Eventing instructor at least twice, including water and ditches. Go to two different places to school. You donât want to be eliminated by a ditch or water jump early in the course. It is ok to be eliminated, but you wonât feel you got your moneyâs worth if you donât get at least most of the way around the course. Find out if your competition course is timed. If it is untimed, feel free to walk if you get lost on course or are out of breath. In a few seconds, you will figure out where you are and be able to trot or canter again.
Good luck! I am 27 and will be doing my first event next month too. Let us know how it goes.