Marketing for the internet is an entirely different field when compared to marketing in the real world. Although, just like marketing for corporations in the real world, many of the same theories apply.
At the start of every business, you should have a business plan. This will undoubtedly be different for different companies and different types of industries. In some cases, you don't have as much planning to do, but in others you'll end up with a 200 page document.
Now, when starting an online business, or even when just branching off and creating a website for your business, you'll have lots to plan. For starters, what type of website works best? Many internet marketers will tell you that first and foremost, you need to have a blog based on your industry. If you're running a company that sells candy, start a blog on how candy is made. This is becoming more and more essential because it turns your website into a living, breathing thing. People will be able to leave comments and you'll be able to receive feedback on your product.
Blogging is a great way to start an online business because not only can people leave comments and feedback, but you can write about other people and others can write about you. This is the basics of linkbuilding. Essentially, the more that other people talk about you, the more popular your website will become, most notably in search engine rankings.
One of the biggest mistakes that online businesses make is to put up advertising on their site. This is fine once you're established, but is absolutely never okay when just starting out. It generally takes well over a year for any business to start making money through the internet. It will be worse for your company to try and force it than to try and make money right away. In fact, using ads can actually hurt your reputation as a legitimate company in the eyes of many online communities.
Once you have everything running smoothly, you should start using social media marketing. Submit your blog entries to StumbleUpon and Digg and Reddit. Get friends to help rate your blog posts and you'll start to see a huge increase in traffic. A good estimate of what you should aim for is 2000 hits per day.