Getting Started In The Field Of Horses

First, you must decide what level of involvement you want. Do you just enjoy the occasional trail ride with friends? Are you a weekend rider who might attend shows for a bit of spice? Or are horses not just a hobby, but a career?

For the occasional rider:
Trail rides can be expensive. Make sure to call around, and get not just the best price: also look for a stable with good horses and good trails, where you'll get your monys worth. Get advice from a friend who rides more regularly, if you can. Or look online for reviews of a farm your considering of trailing at. Riding vactions/dude ranches can also be a good option, and not always prohibitively expensive.

For the weekend rider:
Many stables will allow you to exchange work (mucking stalls or cleaning tack) for weekly or semi-weekly lessons and trail rides. Some schools, especialy colleges, also have equestrian programs. Also look into 4-H and your local agriculture department. Remember to explore all your options and choose which best suits you.

Career:
Usualy, unless you're lucky, you'll start the same as a weekend rider, mucking stalls for lessons. Spend all the free time you can spare at the stable. Be helpfull. In college, you can ride with a colliegiate team (IHSA). This is costly, but generaly a small fraction of normal lesson costs, and a good way to get to know other horsepeople. Always listen to other peoples training methods, and consider how they apply to you. At your local library or bookstore are countless books and magazines that you can take advantage of.
There are a great number of careers involving horses, and just as many ways to go about those options. Vet, Vet Tech, Animal Science, and Agriculture degrees are available at many colleges. There are also apprenticeship and trade certificate programs. It's important to know exactly what you want to do: breed, train, vet, farrier, dentist, nutritionalist, equine massage...the possibilities are endless.