As you may know search engines play an important role in site promotion and because of this there are quite a lot of rumors and old secrets that circulate about those search engines. May be the one that is very common is the so called “invisible text” technique. This is very simple to do, what you need is just to place some text to your site that has the same color as your site’s background and include some keywords there. It is called “invisible text” technique because search engines don’t pay attention to the background color but see the text, while those people who visit your site don’t realize that it is there.
This is a very old method but there are still some websites or pages that use it. Search engines are more effective and now and know how to deal with this kind of manipulation. So if you get caught while you are doing this you can have your rankings dropped as a result of this or even banned from this very engine that revealed your manipulation. So I would just suggest you avoiding “invisible text” technique.
Another trick of this kind that is used for site promotion is adding a very small text to your page that is stuffed with the repeated keywords that you want to target to your site or page. The goal here is the same as the above mentioned method: to hide the keywords from the visitors but allow the search engines to see them. This method is also a very old one and is very dangerous to use it now as it may cause design problems.
Another mistake that is made by webmasters for their site promotion is adding certain popular keywords to their META tags and main texts of the page that are getting searched quite a lot but has nothing to do with the content of their site. They hope that their sites will be seen by many people and they will have quite a lot of visitors. I think that this not a good method for site promotion as it brings those visitors to your site that are interested in something else but not in what your site can suggest them. So sooner or later they are going to leave your site. In this case I would suggest you placing such kind of keywords in your site that are relevant to the content of the site. And also try not to use those keywords quite often in your page as repeating them very often will cause you trouble.
And also one more thing that I would like to mention here is wasting your money on services that are submitting bad services. So I would suggest you first testing them and only pay them if you are satisfied with the results.
I hope I could help you avoiding mistakes that are commonly made for site promotion.