Keyword placement, keyword proximity, keyword density is all important factor in a website development. But overdoing those like placing keyword on every part of your page will do no good for you. These is termed as Keyword stuffing by experts and in terms of search engine it is called keyword Spamming.

The consequences are that your website may get penalized by ranking it low in SERP (Search Engine Result Page).

Don't make your page heavy; mean to say one should not over-use the things mentioned below:

* No heavy Images,
* No Heavy Flash,
* No links in Flash.

One can include the images but in an appropriate manner.

Another factor is cloaking which by far is an important issue as far as penalization is concerned.

Cloaking is an unethical SEO tactic which involves serving a specific page to each search engine spider and a different one to human visitors.

There are three types of cloaking:

1) IP based

2) User-agent based and

3) Hybrid

IP based cloaking involves showing different pages (which are highly optimized with fresh content) to the search engine based on their search engine (IP).

User-agent based means where the spiders' User-Agents are recognized at the server and handled accordingly.

Hybrid is a mixture of the both IP and User-agent.

IP based cloaking is by far used more to serve the cloaked pages to SE.