The most important thing to remember is that horses are individuals, they need time to work in new relationships.
Let the horses get used to each other from a distance, place them in adjoining paddocks separated by fencing or in stalls that have bars on them. I keep them apart for 2-3 days.
When first placing the horses together in a paddock, make sure you have placed several different piles of hay in the area.
The introduction will go smoother if you use this method, this does not mean that there will not be any fighting, but it will be less stressfull for the horses. If you have more than one horse you may want to introduce them to each other one at a time.
