Western and English riding lessons tend to be expensive--financially, emotionally, and physically--so my first recommendation is to be absolutely certain you have a suitable instructor. That means finding a person who is not only knowledgeable but focused on rider safety. My ideal first instructor has a calm, trusted longe horse confirmed in all three basic gaits. Group lessons and/or individual lessons may work well for intermediate riders, but a true beginner is better off not having to worry about guiding a horse while struggling to develop a solid, independent seat. Finding someone who can provide even a month or two of longe lessons gets a neophyte rider off to a stronger, less stressful start.
The oldest student I started was a PhD psychologist who took his first riding lesson when he was 65. He moved away after only a few months on the longe, but he was already confidently using the reins and walking and trotting my longe mare with me acting only as a fail-safe at the end of the longe line. While fairly rare in the US, the Spanish Riding School still puts riders on the longe for many months, and even US Olympic riders often take regular longe lessons. A skilled instructor with a sharp eye can stop problems from becoming hard-to-break bad habits.
As a person who taught herself the basics on a green horse and who fifty some years on still suffers from some seat faults because of that, I put choosing the right instructor at the top of my list. Again, it's impossible to underestimate the potentially devastating effects of even small seat faults.Given the importance of a correct and independent seat, knowing how to interview and select a potential riding instructor then becomes perhaps the largest obstacle in learning to ride correctly and safely.
Luckily, reading some good books on teaching riding can help avoid choosing an unsuitable instructor. First on my list is Jan Dawson's Teaching Safe Horsemanship. She provides advice invaluable for instructors, advice that can also serve as a template for the beginner to use as a checklist to rate prospective instructors. If an instructor doesn't follow most of her advice, I would look elsewhere. Of course, there will be some divergence. I, for example, teach my horses and students to be comfortable working from either the right or left sides. Leading and mounting from the left side is however European tradition dating back to the time men wore swords, so I warn students to expect most other horses to be used to left handling only. However, those who want to ride a horse in Japan will find horses there are worked from the right side because ancient Japanese warriors wore their swords on their backs. Sometimes knowing trivia can prevent problems.
Reading's a good way to pick up both trivia and general principles. Good and great books on equitation abound, so picking the few to start off can be a challenge. Ericka Prockl's Learning to Ride As an Adult: A New Training Method for First-Time Riders could be a good place to start since an actual horse isn't necessary. Her book and an exercise ball can start the horseless student toward a correct, secure seat. Exercise balls give an essential feel--and one can easily watch TV or videos while sitting on one! If available, a mechanical horse is also a wonderful tool. I wish I could afford one, but they're usually found only in big riding centers. They're the ultimate in safety and convenience. Three keywords--mechanical horse simulator--bring up some great videos on YouTube.
One of my favorite riding masters teaches by starting her students on a mechanical horse she helped design. I've given copies of Heather Moffett's Enlightened Equitation: Riding in True Harmony with Your Horse to several of my students. Moffett, while a fully certified British Horse Society instructor, goes beyond their theory and may be considered a bit of a renegade by some because she touts the pelham bit over the snaffle for most riders. While I tout bitless over bit, both of us have the same reasoning--the comfort and posture of the horse as well as the safety of the rider.
Moffett's Facebook page also serves as a wonderful discussion forum, as does that of another English riding master: Sylvia Loch & The Classical Riding Club. I've found the discussions on these two sites to be extremely high quality. In fact, some absolutely top level authorities, including Olympic riders post in these forums. Another Internet resource I use is YouTube. By sheer accident, I found Warwick Schiller there. I recommend pretty much all of his videos because he uses the least force of any reining horse trainer I've ever seen and he starts his horses bridleless. For a sample, I recommend "Bits for Bolting Horses" and "Teaching Collection to People."
One of the few horsemen I've met with a real sense of humor, Schiller's also a keen observer of people as well as horses and a clear interpreter of the theories of the inimitable but often opaque western horseman Tom Dorrance. For sheer fun, I also recommend his "Harlem Shake with Horses." He also has DVDs and a subscription video service that's heavy on hows and whys rather than the promotion of a line of gear.
As to books, dozens of great books on equitation exist. For a short list, I'll recommend a few. Mary Wanless's Ride with Your Mind Essentials: Innovative Learning Strategies for Basic Riding Skills offers a straightforward, well illustrated overview. Wanless also talks about breathing, a powerful riding tool and something most masters of the past likely used without any conscious awareness. For those wanting more detail on, I'll slight Seunig and a number of other 20th C. German masters whose books have helped me and mention Wilhelm Mueseler's Riding Logic instead. Although Mueseler was not a classically trained rider, his Riding Logic provides a clear and relatively brief introduction to the intricate world of German riding theory. For an even better one volume work on classical riding, The Complete Training of Horse and Rider by Alois Podhajsky of the Spanish Riding School still tops my list.
Podhajsky's my hero. Although I haven't cracked _Complete Training_ in years, I reread his My Horses, My Teachers not that long ago and realized how profoundly it had affected how I work with horses. It did not teach me to ride, but it taught me the fundamentals of how to train horses--no force, lots of analysis, lots of reward. Podhajsky and my first difficult horse convinced me to stop riding with a snaffle. My students spend their first year or two riding bitless. When they're advanced enough to graduate to a snaffle, I often hear them say, "Why?"
For many pleasure riders, bitless provides all they need. So far, not much is published on riding bitless, and even some experienced riders don't know how severe some bitless rigs are. Right now, most information on bitless riding comes instructors and the Internet. Aside from natural horsemen like Schiller and Pat Parelli who demonstrate their methods, few other widely available resources exist. Facebook has bitless forums. Web sites such as LightRider Bitless Bridles exist. Hmmm. I may have to write a book on bitless work.
Good luck learning to ride!