You'll have to be a bit more specific about what you're having trouble with. Did you finish the model satisfactorily even if steps 31 and 53 didn't look at all like the diagrams?
Step 31 appears to be a three dimensional intermediate fold that doesn't fold flat until 2-3 steps later (the triangular point is spread-squashed).
For a relatively complex model such as this, foil paper would be the best choice.
Thanks for your replies. I think I have managed with Step 31 now...
But on 53 I dont understand what the vertical dotted line with the looped arrow is referring to?
The vertical dotted line is an x-ray line, so it's referring to a crease made in one of the inner layers.
Step 53 can be broken into two parts, the first to form the leg (the topmost valley fold). This valley fold looks like it needs to be done together with the folds on the left of the triangle - this is a combination of a squash and a sink and a swivel fold. Once this is done, the right part of the triangle (the mountain fold on the right) is folded over, completing the step.
The vertical dotted line is either showing the location of a layer behind the upper layer, or it's a fold that's supposed to take place behind the upper layer. Or both. The looped arrow shows where the layer is supposed to go.
I hate those diagrams. They make you do a lot of complicated stuff with the wings. In the end you just need the points that will form the wings folded in half and then you easily spread and shape the wings. There is no reason to go through all that hassle if in the end you will obtain the same wings with a lot less effort.
I've had a lot of trouble with step 53 as well. It looks like a swivel fold. I can fold it fine but there seems to be an extra bit of business that leaves the two points unlocked so that when you fold the triangle to the left the 'legs' stay where they are. When I fold it over, the legs come along for the ride. Not sure what I'm doing wrong.
UPDATE:: Managed to fold step 53 by a sheer flook.
Please, i need someone to post some photos of steps 30 to 32 done the right way (and some explanation). I tried several times to fold this model but these steps always go wrong.
I am always doing an additional step to accomplish it:
the following picture shows step 30 from the back http://img78.imageshack.us/img78/4315/11yz.jpg
there is a little flap, that you need to unsink. http://img83.imageshack.us/img83/360/21he.jpg
after unsinking it, you will just need to close the flap, fold it downwards and stretch it.
it's not 100% the same folding process, but same enough for me