Online marketing is an easy way to spread the word, and costs less than most traditional marketing methods. However, when using online marketing, you'll want to make sure that the methods you're using are actually paying off, and that you aren't wasting your time, money, and effort using methods that aren't getting you any results.

Here's a list of essential online marketing statistics which you should be checking regularly to gauge the effectiveness of your methods:

Conversion rates. Conversion rates are the most obvious statistic to keep track of, and are one of the most important! Any time you change your sales copy or promotional tactics, be sure to take a look at your conversion rates soon after, and see if the change produced a rise in sales, less sales, or no change at all. You can learn many useful things this way.

Aside from keeping the most effective language and duplicating it on your other sales pages, you can figure out what traffic sources send you visitors with the highest conversion rate and make use of that information by promoting at those places more.

Email open rates. Simply put, the higher the open rate, the better. The more list subscribers that are actually opening and reading your emails, the more engaged your list is, which means they're more likely to listen to you and buy from you. You'll want to test out different subject lines and how effective they are in getting your list members to open and read the email.

Email click rates. Once again, the higher the click rate, the better. A high click rate means that you have an extremely engaged list, especially when combined with a high open rate. Tracking email click rates will let you see what link placements work the best, whether it's better to have more or less links in an email, and so on and so forth.

Twitter link click rates. When using Twitter to share information about your products and services, you'll want to track how many people are actually clicking your links. You can easily do this by signing up for a bit.ly account, and then use that information to find out, for example, what headlines or wordings make people more likely to click your links, and what days of the week and what times of day your followers are most active and most likely to click. Then you can use that information to tweak your tactics accordingly, for the most effectiveness. And, of course, you'll want to track what your Twitter followers do when they land on the link and what their conversion rates are compared to a random visitor.

The real key to effectively utilizing these marketing statistics is to always be testing your assumptions and looking at the statistics to see what the results are. You might think that one thing will raise click rates, when it actually lowers them. Or vice versa. Instead of using vague guesses and impressions to direct your online marketing, use statistics for a better chance at success.