I have only been on five hunts total as a guest of my mom, but from a newcomers perspective these are the things that seemed most important to me:
Originally Posted by horsegirltv
“what are the basic rules for members of the field.”
-If you are new, stay to the back of the field. Have or make a buddy or two that will keep an eye on you, stay at the back with you, and wisper instructions.
-PAY ATENTION to YOUR field Master and the huntsmen and hounds if you can see them.
-Stay quiet, don’t talk unless necessary (asking questions is a good reason to talk), never talk while your field master is giving instructions (pay attention to the instructions!).
-If the hounds are doubling back (term?) and are coming towards you, get off the trail and FACE your horse towards them (again, never risk getting in the way of the huntsmen and the hounds, give them a clear path, even if it means backing into the bushes, DO NOT risk your horse kicking a hound or another horse passing by.
-Stay a horse length away from other horses, you should at least be able to see the horse’s hocks through your horse’s ears. pay attention when a rider is slowing in front of you, they will raise their hand, this way you don’t run up on another horse.
-If you see a hound, DON’T talk to it. If you are worried it has strayed, tell a more senior member who will tell your field master.
-ALWAYS thank your field master, Master of Hunt, and MFH after the hunt!
-Be Safe. If I am getting tired, I find it helpful to bridge my reins and put my feet more ‘home’ in the stirrups and ride in a defensive chair seat, still careful not to hit my horse in the mouth. If I don’t think about this, I tend to get in a more unsafe forward position.
-HAVE FUN b/c IMO it is about the ‘funnest’ thing you can do on horses!
“what are the jobs of the Master of the Hunt, the Huntsmen and Whipper-ins?”
-I’m still not clear on this part. Whips control the hounds I think, keep them together when necessary. The Master of hunt leads the hunt and makes big decisions and the huntsmen are his/her helpers? I’ll keep reading this post to find out 
“what is the number #1 thing NOT to do as a part of the field.”
-NOT Paying attention! It is a hunt, keep all senses ‘ON’. This is for safety, and also, the more you listen, see, and generally notice, the more you learn about the hunt, the hounds, and how it all works. (can’t stress this enough PAY ATTENTION!)
Also, a #2
-DO NOT let your hose kick. And do not ride up on another horse. Keep them in a position where if they do, they will not hurt anyone or anything. If they happen to kick (not sure if you are riding an experienced hunt horse or not) discipline them.
I think you have great 101 questions. Please everyone correct anything I have said that is wrong. I just thought it would be helpful from another beginner’s perspective, since these are the basic basics that I have been taught.
ALWAYS thank your field master, Master of Hunt, and MFH after the hunt! Have fun!