We knew nothing when we started. Let me save you some trouble: study “natural horsemanship” techniques like Parelli and others teach. Knowing how your horse thinks and views the relationship will make everything more enjoyable and safer for both of you.
Also, if possible your first horse should be broke to ride, preferably by natural horsemanship techniques. Many of ours were rescues and some still are not broke to ride.
All warnings aside, knowing horses has been one of the most enjoyable things in our lives.