Too hot to ride? Long-reining and in-hand work require minimum equipment, and can be done in walk as summer exercise. You can dress cooly, but be sure to wear stout shoes and gloves! (A hard hat too is recommended.)
Schooling your horse from the ground calmly in walk gives you time to assess his way of going. It also gives you time to improve your body language and application of your aids, to make sure he/she understands what is required.
For more details, please see my book and accompanying DVD, Lungeing, Long-reining and in-hand schooling.