Arab manes and tails are meant to be kept as long as possible.... you don't want to pull, cut or otherwise shorten except a rare instance when you do a slight trim or even up, but most arab owners rarely do that. It's best to keep them braided up when you aren't showing...usually the main is done up in a running braid (like a one sided french braid down the neck where you only tack from above). Tails are usually braided and wrapped...I do this with Cinny's tail even though he isn't an Arab. You start about an inch under the tail bone NEVER INCLUDE TAILBONE and braid down to the end and secure. Then you double it back up and pull through the top, it should be loose enough where you left about an inch under tailbone. You may have to loop twice if it drags the ground. Then you wrap vetwrap to secure it...again, not near the tailbone, only what is braded and looped through. I take Cinny's out about once a month and in the summer I also loop a fake tail I made out of bail twine through the vetwrap.... you don't want to hook it to the tail itself because if it gets caught it can do some damage...only attach to the vetwrap.
Many people put conditioners etc in their tails, this helps. I like going to beauty supply stores and buying a spray called Hask Placenta...it really helps keep it strong.
I once boarded at a stable where there was a 3 year old Arab gelding who's mane was literally to it's knees and it's tale dragged the ground by a foot! I think this is a little overboard, but I think it's also every arabs owners dream if they are showing. This horses mane and tail was ALWAYS braided up, I only saw it down for shows or cleansing.
Here is a great video on how to do the running braid and keep it in
Here is a good tail wrap video, tried to find a better one...maybe I should make one using the fakey tail LOL
And here is what the wrapped tail with an attached bail twin tail looks like on my horse. tail swatter2.jpg
For showing or just feeling like looking fancy, I would do the running braid and then let the tail flow... Remember the more you brush it, the more hairs break off especially without some sort of conditioner or detangler.