To begin you must be careful to the environment and pose. Because a photo of a muddy horse in its paddock will never have anything delightful. Next, an animal not commanding, it is especially necessary to adapt itself if you want to take it in the "nature". Finally the photography angle counts too.
The preparation phase is very important
Pictures takes planning. First, you must understand that the preparation of photographs takes time, all day if necessary ... and several prints if you want to photograph your horse sublimate and not just make some souvenir photos.
Beware of the weather, the time and the season !
In winter, it is interesting to enjoy the sun of 2 pm : the best of all. In addition, the fresh air will benefit the horse: it will be even more active. In summer prefer the morning around 10 am.
Then you need to start the session early in the morning ... because you will have to thoroughly pamper your horse. Remove any mud, make it clean and trouble mane. Don't clamp your horse, use the halter and the lead.
Where to go to achieve the best shots?
To photograph in "landscape" requires that the landscape is cleared. Absolutely no electric fence background or town, houses ... The floor should be a meadow. In fact if you are surrounded by nature and you know a little isolated meadow that's perfect.
Once on the scene, how should be the horse ?
Your horse must be active. It is better to be two: the photographer, a little behind, and the "trainer" who occuppe enable the horse to bring it trotting forward ears, galloping ... And if you catch it in some acrobatic joy, take in the heat of the action. However, the "handler" should not be in the field of photography. This is why it is important to calculate your location.
See above where the light is best: the horse should not be too much glare but not be dull either.
Try to photograph it of 3/4 and face. Neglect the times when it is grazing.
More information about horses and fine used saddle here !