SEO, if done correctly, can provide a lot of traffic to your website. A lot of people are confused about the trivial details of SEO and in doing so, do not look at the big picture.
Search engines reward behaviour which enhances visitor experience on your website. They penalize anything which is overtly designing to deceive them. Along those lines, this article tells you what NOT to do:
1. Thou shalt not undertake keyword stuffing: There is no rule suggesting how much keyword repetition constitutes keyword stuffing. Think about it like this, if you repeat a keyword so many times that a visitor to your website sees your website as spammy, you are most likely stuffing your keywords. I would suggest not to have too many repetitions of your crucial keywords at all. Just write your content as it comes naturally to you.
2. Thou shalt not cloak: Cloaking essentially means that you are showing your visitors a certain content but when the bot comes to check your website, it is shown something completely different. Do not do this. Even though this practise works for affiliate websites, which generate commisions by undertaking arbitrage opportunities on Adwords, if you have a generic website, it could be disastrous for you.
3. Thou shalt not have the exact same duplicate content: If you have 2 exactly same webpages on your website, your rankings will suffer. So make sure no two pages are similar. Keep different content on different pages. Search engines do not penalize you if someone else copies your work and puts it up on their website (because it is outside your control), but if you have duplicate content on your own website, it will raise red flags.
4. Thou shalt not create the whole website in Flash: Search engines cannot read Flash even though they can index it. So if your whole website is created in Flash, your SEO efforts are probably worthless. So do not do it.
5. Thou shalt not link out to bad neighborhoods: Once again, you are not penalized if bad neighborhoods link to you, but if you link out to them, your rankings will suffer. Before linking out to any website, go and manually check the website to make sure it looks legimiate and is not a link farm etc.
Make sure you do not do anything related to the points mentioned above and you will derive a lot of value from SEO.