Submitting your website to the various online directories is an important part of any Link Popularity campaign. While your traffic from many directories may be minor or irrelevant, relevant incoming links to your website will help in your overall search engine link popularity.
Paying for your directory submission can be a waste of money. You can get just as good a result from submitting to free directories. Personally, I wouldn't recommend you pay for what you can get free elsewhere.
The best directories to submit your site to are Search Engine Friendly directories (those that actually have your site URL listed at some point, rather than outlinks that are simply code). Some will ask for a reciprocal link, some will not. One list of non-reciprocal directories is at http://www.Pimp-Url.com . Opinion at the moment is suggesting that non-reciprocal or one-way links are better, although any relevant link is useful. Directories that do not encode outgoing links will help your website's Search Engine Ranking.
Deep Linking can be worth linking to other pages on your site other than your main page. Before doing this, make sure that the directory you are submitting to permits you to both submit URLs other than your home page (some only allow top level submission), and for the same site to be submitted to different categories (not all directories permit what are essentially multiple submissions of the same website). This will work especially if you have online tools or directories (such as your links page) on your site that are useful and relevant to add to other directory categories. Choose the relevant directory category for your website. Most directories will have many categories you can submit your site to. Decide on the one that is most relevant, preferably a keyword that you are aiming for high search engine ranking in, and try to submit to the same or similar category in every directory, at least for your main page. This will increase the ranking of your site relating to the keyword chosen.
Submit to different categories as long as your website is relevant to those categories. This will increase the number of incoming links to your website. Writing the title for your website is very important. Try to include a keyword you are aiming for ranking in the title, but make the use of it appropriate. Describe your website in a way that will attract visitors. The length of your description will vary from directory to directory, but most will be under 250 characters. Some will allow up to 1,000 characters, and in those cases write the most comprehensive description of your site and its features that you can. It is a good idea to write several descriptions of different lengths, say from under 50 characters for a brief overview, to around 150 characters for a fuller description, up to 250 characters for a yet more comprehensive listing, and finally a full description as previously mentioned for over 250 characters. Keep your listing pertinent to your website, insert keywords where relevant and appropriate, but do not just submit a keyword listing, as most directories will reject your submission. Save all your descriptions in a text file, and just copy & paste into the descriptions boxes when needed rather than typing the same descriptions out again and again.
Again, as with the description mentioned above, the amount of keywords you can use will vary from directory to directory. Some will not give the option, some will allow you numbers of keywords, whilst others go by numbers of characters. Make a list of all relevant keywords for your site, from most important to least, and basically keep adding keywords until either you get to the bottom of your list (unlikely unless your list is really short) or you run out allowed characters/keywords. Check what keywords your competitors are going for if you need inspiration. This can often be done by viewing the source of a web page and checking the META tags. Again, save your keywords to a text file.