If your developing your program in an OOP, make sure you re-name each button - it should provide some info on what it does eg. exitBtn
exit - it tell me that this button closes the program
btn - tells me that it is a button
There are several other abbreviations, like:
lbl - label
tmr - timer
frm - form
txtbx - text box
var - variable
tb - tab
fla - flash
I'll add more.
Hidden comments:
This is possibly the most important thing - adding hidden comments will allow you to see what the code does, and in an error, allow you to go to it quickly. If you are in a rush, you can also find the code quickly and easily.
Code:
It should be organised, so that the code can be easily troubleshooted. DO NOT put all of your code in a clump, as this will make error solving 100% harder.
GUI:
Make sure it is simple, and doesn't over load users with thousands of options If possible, make it that the user can see what he/she ONLY WANTS TO SEE. If there is something visual, like a flash object, make it large so that people can see what is happening.