You'll figure it out when you get it on the board and see how the hide distorts as you stretch it. You'll be taking a 3 dimensional object and opening into a 2 dimensional plane. Think about your T shirts - as a complete item, they'll lay flat, which a hide will not, but you can kinda simulate the shapes by trying to lay a fitted T shirt flat, but not in the conventional way, instead by laying it as if it was on its side - the edge seams together in the middle, sleeves on top and bottom instead of both sides. The fitted waistline won't want to lay flat, and the sleeves will bunch and pucker. You'll have to pull the waistline harder to stretch farther than the chest or the skirt so it all ends up laying flat in the middle. To keep it from puckering, you'll also have to pull slightly up towards the neck for anything above the midline, getting more aggressive as you get closer to the top, and slightly towards the skirt for everything below the midline. In all of that, you have to watch the back line to be sure it stays straight and isn't getting pulled side to side at different parts of the hide. The hips, rump, shoulders, and armpits are tricky, because they have to pull the center of the hide out laterally from the back line, but also must be stretched on their own midline, which can induce puckering at the corners and ripples down the edges.

It's not difficult, but it's a lot more challenging than most people realize before they do it a few times. It's easy to pull the center of a hide flat, but when you're doing a rug, you'll have to be sure you have your edges flat, far enough out to at least reach the hairline transition. Where you start tacking the hide is probably the most important choice, and you might find different methods which work, but ONE which works best for you.

Again, it's not difficult, really, but it's also not the same as ironing a T shirt - unless you're ironing your T shirt laying on its side.