There's only one thing worse than doing no search engine optimisation and that's doing too much. When setting up a website or wanting to promote an existing one, many people go absolutely overboard and begin slamming in the keywords and building up the back links.
Trouble is, if you suddently appear on the scene with a website that's quite obviously trying too hard, Google may penalise you more than if you'd done nothing at all.
Way back in the 19th Century, Britain suffered an outbreak of cholera that threatened the lives of many people living in large cities. London was particularly affected and people were being rushed to hospital and, unfortuanately, dying with alarming regularity.
However, an interesting thing happened during the outbreak. Records show that the number of deaths from the disease was actually higher amongst those who sought treatment in the hospital than those who had none or went for alternative treatments.
How can it be that those going to hospital had a higher death rate? Surely the hospital was using the latest technology?
Well, yes and no. You see they were doing what at the time seemed to be the best way to treat the disease and these treatments included blood-letting and leeches. Nice.
In fact, their methods were useless and actually ended up killing more people than they saved. It's believed that they made things much worse by reducing the patient's tolerance to the disease. By trying too hard, they actually condemned many people to a pretty nasty death.
Ok, a gruesome analogy, but you get the point? Doing too much of anything that's supposed to be good for you can end up with bad results. In the case of SEO, if you go crazy and try to ram too much work in, you're on a hiding for a banning from Google.
Reign it in, do it slowly, it'll happen in the end.