Can your horse go on the bit and be collected? If yes, work on your trot work and staying consistent with being on the bit in both walk and trot. If that's consistent you can try cantering and do the same thing, consistency is the key with being on the bit and with tempo. In dressage being on the bit doesn't just mean having their heads tucked in but also moving forward and tracking up. But if you wanted to just try a competition for fun showing intro level dressage is a great choice because your horse doesn't need to be on the bit in this level and all you need to concentrate on is keeping your horse forward, tracking up, and even in tempo. Intro level is only walk-trot, and it isn't just for kids either
. The next level in dressage is training level which includes canter transitions but your horse must be on the bit at all times. Hope this helps.