Well first going out from the ground of course. In order for you to understand firstly the horse's behaviour and emotions in that situations and also so that you can reassure him.
I would suggest exploring on a long rope so he has space to look around and you have enough rope to control the situation if he runs off.
As already said when mentioned follow one or more confident
Yup! With another horse. In areas that your horse is familiar with as well.
Go out with another confident horse (: