Spiders vs. Eyes

What can the eye see that a spider cannot?

To make this simple, consider this: A search engine spider can only read textual content, and it can only rank your site based on what it can read. So anything other than textual content on your web pages is merely clutter to a spider.

With that in mind, go to any web page and look at the HTML source instead of the way the page looks in a web browser. Now imagine that you have never seen the actual web page, and have to judge how well that page should rank on a search engine strictly by what you can gather from the source. For example, look at the following:

1) (An Image)

2) (Text)
Fly Fishing for the rest of us

To a spider, #1 looks like this:
<img src="images/flyfishing.gif">

and # 2 looks like this:
<font>Fly Fishing for the rest of us</font>

If you were a spider, which of the two would you better understand?

The point here is to avoid using images where it is not necessary, or at least balance images with strong textual content. However, at minimum, when you have an image, you can enter some alt text. For example:

This code reads:
<img src="images/flyfishing.gif" alt="Fly fishing for the rest of us" >

Avoid frames like the plague

Many sites use frames to make navigation easier. The problem is that most (if not all) spiders cannot read your frames pages. They merely see the main frames page which calls the other pages. The content simply will not be indexed.

Flash

Flash is great, beautiful, and often fun. But like images, a spider will only see the call to the flash, and none of the actual flash content. This can easily render your website impossible to index.

PDF and DOC

Some engines can now index Adobe PDF files and Microsoft Word documents. While we have no evidence that these can help or hurt your ranking, at least these files can now be indexed by some engines.