One thing that helped me was to find a place where I could measure off one mile that I could travel at a good pace. That allowed me to learn what a 7mph trot felt like (takes 8.5 min. to trot) or a 10 mph (which takes 6). That made it easier for me to understand the training articles I was reading. Unless it's on a toll road, it's free.
You need to know not to skimp on your farrier. Skimp anywhere else, but not there. It's hard for me to imagine that before doing endurance there was a time when I was young and very foolish that I had the farrier put shoes on, then called him when they fell off. >shudder< If you're riding that horse a lot you can't leave them on there after that angle gets off. Different horses grow at different rates...and the same horse grows different in summer & winter. 6 weeks is average for my horses though. This will cost you plenty.
Keep a saddle log. It doesn't cost you anything but will help you set goals and stick to them. Having a training buddy will help you to drag it on out of bed on those really cold mornings since you are both trying to show the other how tough you are and refuse to back out of riding.
Control your enthusiasm. If you've joined the endurance community you have made a life choice. It's a long term commitment. You have the rest of your life to meet your goals and this game is one of those that has a lot of squares that when you land on them say "return to the "GO" and start over". The slow way is the fast way. Take your time. Sure, 2 years is a long time to get a horse started, but 6 months and start over, six months and start over, six months and start over... takes a lot longer. Enjoy the journey. Learn everything you can as you come up. Winning is not the goal... that may be the last part of the goal, but it's *not* the whole thing and if you aren't careful you'll forget to enjoy the other 95% of the sport.
Don't make the mistake of thinking that the people in the back aren't "that good" at this sport. I can point out quite a few people riding at the back of the pack now who were the BIG hot shoes when I was getting started. These are people who made very good horses, ran up front, and when the horses slowed down they decided to stick to that horse and do what he could do *now* instead of trading him for another. Others are past winners who are starting new horses slowly. They'll be the big hot shoes in a couple of years. You can learn a lot from them and they'll enjoy helping you out. They don't charge anything.
If you see a campfire, go to it. Stay late. Listen. Meet everyone. They're free.
Never say "this horse never gets tired". Even though we said it when we were getting started and will forgive you if you do. Forgive us if we smile though. We're remembering when we said it and thinking how dumb that sounds now.
You may not be an expert on saddles, but you can watch *dilligently* for any sign of rubbing of the elbows or girth area. Do not feel that you don't have time to let any small wound heal. Believe me. You have time. If you have a regular western saddle, you can move the girth back by running the cinch down to the girth, then coming up and tying it at the back ring. Go ahead and remove those rear girth straps. Doesn't cost a thing.
You ALWAYS have time to stop and adjust your tack. Do not ride through the pain. Fix it now. Lengthening your stirrups a notch will save you money you would spend on Advil.
Don't drink carbonated drinks during a race. They blow up when you shake them...even after they're inside you. :-P Puking them up is a waste of money.
Look at your horse's expression. Is he having fun? If he looks dull, give him time off and back off. Believe me...YOU HAVE TIME. Time is not money...spend it freely.
A stethoscope is handy. Learn to use it so you can volunteer as a pulse taker at rides. It's like reading other people's mail, very informative. They don't pay you, but they don't charge you either. Learn your horse's resting pulse and check recoveries. In the beginning, it may be fun to borrow a heart monitor so that the training articles will mean more to you. However, other than to find out, "yes, we were trotting along at 121" etc. it was of little use to me. I've owned two. Very seldom use one. I agree with Laura, I'll take the "feel" and expression every time over a number. If they come up with a gut sound monitor, I'll use that. That seems to be the hardest for me to "feel". The "feel" method is free, unless you consider time money, in which case you have to make an investment to get it.
I *wish* I could have gone to equitation clinics. I think getting ourselves in shape and learning how to use our bodies with the least tension is the number one thing we need, but the one we're most likely to skip. I want dressage lessons but they're expensive. My daughter is taking now and I eavesdrop. Pain is NOT gain.
I think the number one thing a newbie needs is patience, drive, (you have to balance those two) and an obsession with the comfort of their horse. You can't buy that in a box. If you're saying, "But I'm 42 now...if I do 2 years of LSD on this horse I'll be 44!" All I've got to say is, "How does 44 and starting over *again* sound?"