In my experience, it comes down to knowing your target, knowing what you want them to do, and being smart about how you allocate your marketing resources.

For example, I've seen a lot of companies focus on getting people to the site without a plan. Once someone discovers your site, what are you doing to keep them coming back? Are you requesting them to submit information, presenting them with a unique offer or message, or do you just want to see what they do naturally?

The second thing is measuring your efforts. Every channel and tool that brings in visitors can be measured and quantified. While you shouldn't purely base decisions on the data, they can provide some very good direction on where you should be focusing your efforts.