This is a fairly common problem with almost anything that comes in a reusable bag (sleeping bag, etc).
I did this Instructable with the smallest tent I own, which I got for free from a friend who lost the poles, and didn't want to have to deal with it (you may recognize it from my first one). This kids tent is now part of my hiking gear (AKA - Go bag) since it weighs about 2 pounds.
The instructions work the same for this one as my LARGE family tent. Seriously it's actually just way too big (TWSS). But I was just not wanting to set it up just to prove I could repack it.
Really not rocket science and I think most outdoors types have their own system for accomplishing it. But this is mine.
Step 1: Measure the Tent and Bag
In this case my bag was right at 20 inches. One of the dimensions of your tent will always be roughly divisible by the length of the bag. Since my tent is 60x72 (5x6), I know which way to fold it.
And since 60÷20=3, I know where I need the folds to be. Every 20 inches.
Step 2: Banish the Math
Ok that's not exactly complicated math, and I did graduate college (Go Racers) but you know I don't actually want to do mathematics when I camp, regardless of ease.
So I took a Sharpie and made marks at 20 and 40 inches. This way I always know that it will fit once I get it rolled up.
Step 3: Fold It, Roll It, Sit on It
Ok so we have it folded. I fold mine over a couple of times because rolling it all the way seems like a pain. And traps more air.
After its folded like photo 2, I simply sit on it. Yes it holds air, but it is hardly airtight. It will seep out in a few seconds and flatten nicely.
Then I roll it up tightly.
Step 4: Moment of Truth
I had to move my little operation because rain was moving in. But that's the same rolled up tent and bag.
I had to sit on it again. But other than that, no problem. The poles and stakes are no problem to put in. I actually add them first.
But as I have mentioned, this is now my emergency/hiking tent. No poles.