I shoot 3D all summer long with my family- it is a LOT of fun. The most difficult part is judging yardage. The only way to get good at that, is to do it often. I joined a summer 3D league- it was very relxed, only half the people turned in score cards and it was incredibly fun. I improved at gauging yardage fast.
The second most difficult part-- figuring out where the kill zone is on some of those animals. As said before, a set of binos is a good idea. On your first couple times out (so long as its a fun shoot) its not a bad idea to let someone else shoot first so you have an idea what you are aiming for.
Also, its not any fun to hunt for arrows in the woods and you will get frustrated fast if you keep losing arrows. Until you get some more practice in, move up to a more comfortable place to shoot if its a difficult shot. You can even use the kids' stake on some shots. Again, make sure this is a fun shoot only, or dont turn in a scorecard. Challenge yourself as you get better.
You will most likely find that more experienced shooters are willing to answer questions or help you if you need it. Most are happy to see new people joining the sport. So relax, and have a great time.
And welcome to our world.
