I am not a lawyer. The following advice is worth what you paid for it. :)
I'm going to college next year and I need to start looking into ways to pay for my horse. I want to lease him out to someone. I also want to do some lessons with him and train horses for extra income.
1) Are liability release forms any good? Everyone seems to say they are worthless but people always want you to sign one when you ride their horse. Is it better to do it just in case it might protect help?
Laws and proper wording vary by state. Best to check a lawyer in your area. He/she might be able to give you some tips or standard forms for little or no cost.
IMO, any form is better than no form.
2) What kind of insurance should I have if I'm giving a few lessons (on the property where my horse will be kept) and training several horses for others (on their property)? How much does that cost on average and what are the best places to get it?
Trainers insurance is what you need. By giving lessons you are acting in a "professional" capacity. Your liability is increased and you need proper insurance for that. Contact an insurance agent. If the property you are operating at is a commercial facility, they may have a policy you can be added on to. If it is not a commercial facility and you are running lessons there, they _should_ get a policy to cover what you are doing.
3) Besides having good insurance and always taking precautions such as helmets, etc. is there anything else I can/should do to protect myself?
If there's anything else I should know, tell me! This kind of stuff is always a little confusing for me....
I'm also not 18 yet; I am aware you can't have insurance or anything until you are older than 18 but I wouldn't do this until then anyway :)
You can be insured while under 18. Not being an "adult" you simply can't enter into the contract. You need an adult to purchase/sign the policy and add you as a covered individual. This is probably something best done through the property owner since they should have insurance to cover your lesson program at their facility.
A really good place to start is an insurance agent who deals with equine/farm policies. They will explain the insurance options. They will also have liability forms for your students to sign. Generally, an insurance company will want to see your liability release form to make sure it meets their standards. Often, they will be able to provide you one for use.