Re:"I have no clue how to write a good one." (Score 1)

Doesn't matter, neither does anyone else.
There is one important rule in creating a GUI: follow the same design principles as the target OS and applications with similar functionality as yours.

That's a strange couple of sentences to string together...

I've found that really understanding the situation(s) the program will be used in is fundamental. Good user interfaces just fit with the situation, and feels second nature. Too many toss inn all the info and controls that they can into each window, where a better understanding of what the user need in each scenario would allow to remove most of it alltogether.

Also, consistency is king. So do adhere to good recognisible style.