Comment your code
It doesn’t matter if you write proprietary or open source code, comments in your code are very important (somehow even more important than readability and functional correspondence to the client’s needs). This is especially true if someone else is supposed or will, one day, look at your code, re-use your code and/or build upon your code. For example, despite the fact that this source code header explained what the whole source is doing, you can’t tell what processing is done in this paragraph: ...