A long, long time ago there were so few websites that almost any site could get traffic as soon as it got indexed.
That was then. This is now.
You can spend hours, days, weeks or months on your website. You can get crawled by the search engines but getting a real human visitor to visit your site, let alone spend money when they reach it. Dream on!
So what do you do?
You don't want to waste those precious hours you've already spent on your site.
For starters, you need to treat each and every visitor like royalty. If their first reaction to your site is to press the back button on their browser then you need to tweak the design. Chances are that your web stats program will give you this information - how many pages they viewed, how long they stayed.
It's in these stats that the gold lies.
Check the keyword phrases that your visitors used to find your site. They will be really specific phrases. Such as "old mexican silver coins" rather than "coins". Build on this. If your visitor was keen enough to type more than a couple of words into a search engine then they were really serious about finding information. Give them more of that information (which in itself will increase your traffic). Sell them something relating to what they were searching for.
For instance, on the phrase above you wouldn't want to waste that traffic for a few cents from an Adsense click. These people are likely to be buyers! Find an affiliate program and give them a reason to click through to it so they can quench their thirst for buying the product. With the added bonus that you'll get commission as well.