dont ever use keywords that your site is not about. thats the worst thing you can do for seo is to stuff a bunch of non related keywords on your site
Do not Take link in non relevant sites Do not build links huge at one time. Don't use black hat ever.
Don't post 1000 backlinks one day and then do nothing for the whole week. It make things look unnatural in google's eyes.
NO black hat strategy at all, but honest and quality work with SEO tools. Everything that extra is not good in any work or activity.
A big no-no in doing SEO is having hidden links or texts on your website. These are texts that are not visible to your readers' eyes because they have same color as the background. You should never have that to avoid the search engines to penalize or ban you. You also have to avoid content duplication as search engines love original content very much. You should also never do doorway page; it is a page that directs your visitors to another website rather than the one they clicked on. That is misleading people and the search engines does not like that at all.
Don't try to trick the search engines as a means to rank better (ie. no cloaking, no keyword stuffing etc..)
Yes, tricking the search engines and cheating your way to gain top ranking is really bad for SEO and will only jeopardize your website. It is good that there are forums like this to make the people aware of what not to do in SEO. You can even learn about this by reading articles you can find on the web.
don't stuff your keywords... don't put too many keywords on your site... you might get penalize for keyword stuffing.
Your question is very broad and there is lots of answers to your question. There is a lot of do's and don'ts in SEO. I would suggest going on Google and search for "Black Hat SEO Techniques". These are the things you should absolutely not do in SEO.
Dont create huge links in one day Dont create links/comments on no follow sites. Dont do blackhat stuff.
Don't follow any of the advice given by SEO Kiddies on digitalpoint (...unless you are one of my competitors).