I could go on and on and on ...............but I won't. Heres a couple of starters.

The one thing always emphasised by Google execs is be sensible and don't do anything you would not like if you were a Google Cop.

Don't try to decieve a Search Engine by showing the S/E something within the body tag that the visitor cannot see.

In other words don't take the p***

Another important thing to keep in mind is if you steal an inch today and gain an edge, when (not if) the algo is tweaked that inch you stole will lose you a mile.