Don't take Short Cuts.
Implementing a successful Search Engine & Directory strategy is both difficult and time consuming. Therefor it is very tempting to take a few shortcuts here and there - but don't do it. I know because we tried and it simply lead to poor results. At the end of the day we had to go back and redo the process properly anyway ( not only costing us double the time but also meant that for a few months our business didn't benefit from all those 'Ready To Buy Visitors' ! ).

Mass Submission Services
You have seen the adverts, "Click here to submit your site 300,00 Search Engines".
As you have seen, the submission process Must be done correctly or all your previous hard work will be for nothing !
These programs use automated software to blast your details to every possible submission page they can find. Sounds ok, but the major engines and directories have become wise to this and many now have devices in place to block such submissions. At best your page will simply be ignored by the major engines and at worst a major engine may end up Banning your Whole Domain !

Doorway Pages
Much has been written about creating specific 'Doorway' pages to target a particular keyword or page. A doorway page is an exact replica of your main page but which is optimized for a different set of keywords / phrases.
In the early days this worked very well and the major search engines and directories were comfortable with it. However as with most things, advantage was taken by many and soon many pages were produced optimized for certain keywords / phrases which had little or nothing to do with the real subject of the page.
Therefor Search Engines & Directories view such pages as a kind of 'Spam' and as such by using this tactic today you may well get your whole domain banned.

Don't target Keywords just because they are Popular.
It may be tempting to go after the 1,000,000 visitors searching for "web design", but if your product or service is nothing to do with Web Design then you are wasting both your own time and that of your visitors. Think about, if you are looking for help with Web Design and you search for this, click on a result that takes you to a page which is really trying to sell you a book on gardening, within a second you will be hitting the back button and going to the next page on the Search Results. Yes your visitor count will go up, but your Sales won't !

Don't Believe Anything until you see the Proof !
Ok, sometimes you do have to try an activity before you know whether it will work. What we are trying to say here is, view all claims initially with skepticism and before embarking on a particular activity or purchasing a service, thoroughly research the methods and try and understand how it will ( or will not ) lead to increased sales or popularity.
There are many cons and people who don't fully understand what they are doing and so a little vigilance and upfront questioning will usually ensure you don't use a bad or damaging service.