To make paper models you need some things. Paper being the obvious, but further? Glue, scissors, a knife, desk, coffee, comics?
To design a model other tools come in handy. Here is what I use and I would love to hear what others use, we might learn a thing or 2.

Designing:
Adobe Illustrator is my friend. Turn on the grid and set it to centimeters with 10 divisions (creating millimeters). I use the snap to grid function to make sure everything is the right shape. I print at the lowest quality on cheap 80 grams paper for all the test. Measuring the parts before cutting shows you immediately what doesn't fit and should be changed. It save you a lot of cutting.
Of course the final prototypes are printed on top quality and 160 grams paper.

Making:
First I score with a scoring pen and a ruler. It makes the folds so much smoother! Most is cut with a small pointy scalpel and round parts with a small scissor for paper.
For glue I use UHU super power glue and sometimes a Pritt stick (for parts that need glue everywhere). A long toothpick helps to reach the parts that your fingers won't.

That is about it I guess.
Let me know what you guys do!