These are five rules that I think all software how have/do:

1) A clean look - I think all programs should be clear and easy to use UI.

2) Make it do its job well - If you start any project, don't make into a half-ass project! It should do its job(aswell as have some other nice, non-essential features) and do it well, so people say "Damn! I'm gonna tell everyone I now about this and the things it can do!".

3) Good help files - Always make a help/support section so idiots won't have to bother you and they'll have another reason to tells others.

4) Plan before you make it - before you make a program/website/whatever, plan what you want to happen after you've finished the first version. With this, you can code the program and after when you want to upgrade/update it, you won't have to do some crazy re-writting were you have to change several hundred lines.

5) Don't over or under comment - If your gonna be distributing the source code to a program you've made, don't go mad commenting! If you do, your program will turn out to be unnessesarily clottered and will become more comment than code! But if you under comment, the reader of your code may not know what's going on in the program . Just comment lightly but in the nessesary places.

I've probably left out ALOT but those are the ones at the top of my head.

Thanks for reading!