There is nothing inherently wrong with telling your dog “no,” except that it doesn’t give him enough information. Instead of telling your dog “no,” tell him what you want him to do. Dogs don’t generalize well, so if your dog jumps up on someone to say hello and you say no, he may jump higher or he may jump to the left side instead of the right. A better alternative would be to ask him to “sit.” Tell him what you want him to do in order to avoid confusion.
There is an ever-growing list of agility sanctioning organizations. The ones you’ll hear about most often in the US are NADAC, AKC, and the USDAA (see below for a more complete list of national and international groups). Each organization has its own rules and style. For example, NADAC courses are spread out and focus on speed. They often challenge the handler to send their dog through the course at a distance. USDAA courses are “tighter” and more technically challenging.
If a dog has a clean run without any faults, it’s called a qualifying run or a “Q,” and they’ll get points added to their official record. If they get a good score, they may also receive a placement ribbon. Winning a first place is a lot of fun, but in the grand scheme of things placements don’t matter until you reach high levels of competition. However, the Qs are important – with enough points, your dog will earn a title. A title is a certificate of accomplishment. As you earn each title you stick it to the end of your dog’s name, so Fido’s name can eventually start to look like Jonas’s. Very snazzy.
Remember that training is an ongoing process. You will never be completely finished. It is important to keep working on obedience training throughout the life of your dog. People who learn a language at a young age but stop speaking that language may forget much of it as they grow older. The same goes for your dog: use it or lose it. Running through even the most basic tricks and commands will help them stay fresh in your dog's mind. Plus, it's a great way to spend time with your dog.