Due to the high calibre of equipment, fine details can be picked up in a photo, this includes stray hairs, dirt, grass/stable-stains and debris from feed, a nice green mouth is a popular one (the horse, not yours!). It's really important that you spend as much time as you can prepping you and your horse to 'show your best side'.
If weather and facilities allow, a good bath, groom and plenty of elbow grease are recommended the night before.
Plaited, hogged, or au naturale; accessories, bridle, driven, ridden, in hand, head collar or 'naked' (again, the horse not you !!) It's your choice, but be mindful that you pay for your session with time limitations.
Now then, let's speak hats... The health, safety and welfare of you and your horse is your responsibility - some people believe that certain photos astride your trusty steed will look best when posing without a safety hat. I can only stipulate this will be at your own risk - I cannot be held responsible for your decision, nor would I encourage you to do so for the sake of a photo.
My services cover a wide variety of reasons for you wanting photographs including sales, marketing, gifts, personal use and of course to have memories in your home to treasure for a lifetime. The attire you choose is entirely one of personal choice - I'm happy for you to be dressed in a ball gown, tweed or perhaps show gear or all of the above if time allows! I'm also happy to give my opinion on colour schemes that would work well with the colour of your horse or the location.
Most of all, this is about you enjoying the experience, having a bit of fun in making some great photos to share.