There are a couple of design criteria to be met.
1) The user should be able to input the number easily, including scenarios such as copy/paste (which I use all the time) and easy correction of their typos. There are many ways to infuriate the user through little annoyances here.
The chunks-of-four approach should brace for these issues:... (more)
I would start by looking at existing UI that you like and dislike, print it out if you like and thoroughly analyze what is and isn't working for you, what was easy to accomplish and what tripped you up.
After you've done this for a while revisit some of the designs you had trouble with, try to think of what the simplest change you could make to improve them, ... (more)
I saw a web form once that did the following—
"When you do things on the site that you want other people to know about we say something like 'Sam shared his location' or 'Janet uploaded a picture to her album' how would you like the site to describe your actions?"
And the choices were his/her/their... (more)