One easy thing that I've done a lot is to get a packet of carbon transfer/tracing paper. I get mine at JoAnn Fabrics for about $5 for a packet.
Then you can go online and find whatever picture, clip art, image, etc you want. Print it out, set the transfer paper between the embroidery fabric and the printout, and trace over the image with a ballpoint pen.
Now you have your image on your fabric! I usually go over the image with a very fine Sharpie pen so that it doesn't rub off (it won't show through when you're done).