If you want to increase you website traffic, the only way you can do this quick and effective, is using keywords that are specific to the website main theme. In this way, you target specific search queries, what makes possibility to get a click on your website higher.
So if you have a health related website, there is no point to use general keywords, as "medicine" or "pharmacy". Because there are hundreds of millions of webpages that have this words. And if your website has a page rank less than 10, it will just get lost in search results and their will never be a click from the search engine.
Example: there is a purpose to increase traffic of a webpage
http://medicationssuppliers.com/add-url-b2b-directory.html from the health oriented companies.
There is no use to write "submit URL for FREE!!!!!!!"
We write "add medical URL for free", "add medical supplier for free to health directory"
It is also useful to add words as "Blood Pressure Management" or "Diabetes Care Products" - specific words that are included in the directory.
Only thousands are writing "Diabetes Care Products" and people, are looking for this are really looking for diabetes care products. This way there is a chance for a website with PR 3.
If you add a word "Immunoglobulins" to your keywords, there is a chance, that there will be a click one your website. To the webpage with PR less than 10 and with keywords "Submit URL" - there will never be a click!
This way chance to get a click from a search engine is more than 0.