Firstly, I did try to design the paper toys to be as simple as possible. After a couple of test builds it may be worth clearing up a couple of points when building.

Head:
Surrounding each element of the models is the flaps that need gluing. Ensure that the flaps are glued to the inside of the model wherever possible to avoid them showing.

Arms:
What makes these fiddly is that they are double sided, but to make it easy you can simply just cut each arm (with it's flap) out without the back of it at all, no one needs to know.

If you want them double sided then the key is to cut each arm out with both sides as one element, do this roughly allowing a margin of white space. Now fold in half down the middle, glue together, now trim off the excess white space. You should have a perfect double sided arm. Treat this element like any other now, fold back the flap to one side and glue to the correct side of the body (marked with an L or an R for left our right)

Please note this method is used for various elements including Sully's tail or buzz's wings

Body:
The body was designed bottomless, this should help getting a finger inside to aid with sticking the flaps down and gluing the arms against it

I'll work on this post to make it clearer but if there is any problems or questions in the meanwhile then just post it in the contents below or ask me on one of the social channels

Kev