My tip is this; advertise but advertise smartly, not necessarily costly. I have actually been involved in Internet marketing (i.e. selling online) since 1995 which is practically the beginning. I can tell you how often I've fallen for costly advertising that results in no sales.
However, you can avoid some of the mistakes I made my reading the following article I came across less than an hour ago titled "Which form of advertising is more effective" by an expert in search engine marketing/optimization. This is an unsolicited endorsement.. I'm happy someone finally wrote such an article as this news that exposes the lot of the underhanded tricks companies -even reputable companies such as Yahoo.com- are using to what amounts to stealing their customer's money.
The URL to the article is...
http://www.seobook.com/which-advertisement-more-effective