There is a simple way to remember.
In short, where there is only one lead attached to the battery ensure it is the positive one.
Hence, when removing leads remove the negative first (leaving the remaining one positive lead in place before then removing it too). When attaching leads attach the positive lead first.
The same applies when attaching and detatching jumper cables – attach the positive cables first and detatch them last.
The reason is that when you attach the negative lead this is the most dangerous time since the whole frame of the car becomes effectively the negative terminal and hence accidentally touching the positive lead against it will cause a short circuit. Hence, don’t keep the negative lead attached when the positive lead is free to move around and potentially touch the frame.
Hope this helps! and for more cheap truths about free ways to lose weight see the other posts on my blog http://www.gichow.com.