Try to find local schooling shows and go to many of those for experience/learning. The judges are easier on you and you can learn while you show. They can be quite fun. They have green rider classes, walk/trot classes. Just do what you both are comfortable/good at and go from there. When you are both ready to do canter, there will be advanced schooling show classes for you to enter. You can look on craigslist, tacktrader and other classifieds to find good deals on show clothes. Some people have brand new or hardly used items on there that they just want gone. You should also look up horse show etiquette via google or in a horse book to learn what not to do at a show, just so you know ;) Good luck and have fun!
John 14:6 - Jesus said unto him, "I am the way, the truth, and the life: no man cometh unto the Father, but by Me."