In general, we depend on our eyesight more than any other of our senses. Something like 70% of our brains is involved in processing visual stimuli! So it's not too much of a stretch to say that if you can command a person's eyes, you can partially command their awareness. Street magicians take advantage of the idea that sight is so closely related to attention in order to pull off their tricks, and parents of young children, and pet owners as well, use the connection to entertain and distract upset or hyperactive ankle-biters.
As a business owner, you need to command your customers' eyes and attention too, but not because you need to distract them or trick them. You want to make them aware of all the different ways your products or services can help them, or bring their attention to the really awesome deals and discounts you have going on. Whether you're revamping the look of your website, or creating an ad, a poster, or a flyer, you can use these simple design tricks to draw the viewers' attention to the most important information.
Arrows are the most obvious way to direct attention. They get to the point and are best used when you know for a fact you won't have your viewers' eyes for very long. You can use arrows to highlight a process, and give viewers a 'schedule' of sorts for what is going to happen, or have an arrow next to your CTA to make it stand out as the next thing to do.
The arrows in the picture naturally draw your eyes to the right, and the bunching of a lot of arrows suggest the idea of movement, similar to a school of fish.
Pathways and Lines
Paths and lines are similar to arrows, in that they suggest movement, but are much more subtle, so you can have a few more of them in a smaller space without making the space seem cluttered. They trigger the brain's natural curiosity and make us feel we need to follow them, because they could be leading us to something grand.
Triangles can serve as a sort of cross between an arrow and a line. Because they're a geometric shape, they won't be quite as glaringly obvious as an arrow, but they still draw the eye in the direction they point, so you can use them as a design tool.
Faces and Eyes
A face is one of the easiest things to recognize, even if it's not there at all, because they're one of the first ways we learn to communicate. So when we see a face, we immediately pause to study it, in order to find out what this person is saying to us. If face is staring back at us, it's trying to make a personal connection with us through eye contact, and that attempt at personal connection holds our attention and focuses it. If the face is looking elsewhere, then we follow its gaze, because we understand that the fact that this other person is looking at something else means that it is important.
Color and Contrast
Where arrows, pathways and lines lead viewers' attention, color and contrast focus. If the background of a photo is mostly one color, or of the same color tone (all pastels, or all 'natural' colors), our brain tells us there's nothing really important back there, which heightens the importance of the object that is a different, contrasting color. The photo of the eye above does a great job at combining this idea and the previous one. The eye draws our attention because it's a familiar symbol, and the color draws our attention because it stands out against the black and white background.
The next time you need to design a webpage or anything else, keep these concepts in mind (in view?), and use them to direct your viewers's eyes towards a satisfactory goal, for both them and you.