Should we condone or condemn clip art?
Though a professional designer, I use the same old elements every single day which I did not create out of my own head: the dot, the line, the color spectrum. I just manipulate them. The same goes for some everyday clip art. (The absolute best retro clip art is at RetroClipArt.com.) Rather than discarding any thought of using clip art in your layout, stop and consider this:
Clip art can be a conceptual element that establishes a theme. Take for example this little guy on a PowerPoint slide (it’s actual clip art from the 1940s). This first slide looks like the typical amateur PowerPoint presentation, but you’ll see how it evolves into a professional, powerful design.

Nothing screams “clip art” louder than a square white image against a colored background. Simply removing that field of white will take away the amateur clip art look and turn the design into something that reflects an actual layout from an earlier period in time, around the 1940s. (The font isn’t authentic for that period; we’ll get to that later.)

This is a vast improvement. Still clip art, but used professionally. In the earlier days of advertising there was a lot of clip art; but only art directors and designers had access to it, so it was being used properly.
We could stop right here, save for changing the font. But let’s take this a step further as far as layout goes. This is a presentation about communication, so we had better make sure it captures attention and communicates!
Location, location, location. Rather than shouting down into the corner of the frame, let’s direct the voice toward the message itself:

Yes, we can clip the clip art. Cropping and enlarging has made this illustration more powerful. Let’s take it a step further by modifying the clip art itself.
How about adding some color?

Might as well get creative with little touches, like filling the megaphone with a brighter gold than the man. Now, since we’re punching up the megaphone let’s go all the way.
Tear apart and manipulate the clip art further:

The larger megaphone and searing red voice from deep within add to the effectiveness of the illustration.
Now we need some typography that matches the style of the illustration. I’ve chosen two styles that were popular in advertising during the 1940s: Kaufmann script and Kabel. The weights and sizes are well-balanced here, with emphasis given to the appropriate word. It is singed with the same red that is emanating from the megaphone.
Placing the text in front of the illustration gives it further emphasis and dimension (it would be in front if it were a real sound). And coloring the script black, the less important copy, further emphasises the word “communicate.”

I can’t imagine another illustration conveying the message so perfectly as this.
Clip art does have its place, and that place is in the hands of a professional designer.
Look beyond the square jpeg of the next piece of clip art you consider using. How can you manipulate or customize it to become a powerful, integral element in your layout? What can you do to the rest of the layout (colors, fonts, etc.) to enhance the clip art?
The finest retro clip art I have found is at RetroClipArt.com. The styles are authentic, and they are vectorized with transparent backgrounds so your work looks professional from the start. I admire their dedication to authenticity, quality detail, and perhaps most of all giving homage to the great designers of the period. Treat yourself to some spiffy zinc cuts from the era of letterpress, at RetroClipArt.com. (I am not compensated for this plug, other than the fact that I am glad these perfectionists exist!)
See clip art used right at AmperArt.com
My series of AmperArt prints makes use of the same graphic element over and over and over: the ampersand. The whole series is based on the ampersand. You’ll see some standard clip art put to good, imaginative use in this series. Check out AmperArt.com.