How do you make a tower using 30 popsicle sticks and 6 ft of masking tape. The tower needs to be as tall and stable as possible. (it needs to stand straight for 4 days)
Start small, then work on making them bigger. Come up with your own designs, see how they work. Study the designs of other structures. Try modifying them to see what you can make better and what doesn't work. Build lots and lots of towers.
Even if you were handed the "perfect" design on a silver platter, you will still do a much better job actually building it once you've had all of the experience.