Tables are just like any other HTML, always remember "LIFO",
Last
In
First
Out. Some other important things to remember, you can only nest tables inside of <td> tags, and when using colspan or rowspan, the number you use for colspan or rowspan INCLUDES the current table cell you are applying the attribute too. It can still get a bit confusing for me sometimes so for complex tables I usually cheat and use Dreamweaver to basically draw them :p.
Practice will make perfect though... once you've sat in your chair for 10 minutes, scratching your head trying to figure out whats wrong with your code and are about to take a baseball bat to your monitor, and then you finally see where the problem is, you will remember it

.