First, for your examination, a randomly stamped birthday card:
Copyright Stampin' Up!® 1990-2006
View the card and see the supplies I used here, at my gallery: Happy Little Birthday.
Now, what's the secret to making a "natural" looking background like this? Stamping in triangles! It keeps you from making straight lines or rows of images. If you look closely at this card, you'll see how there are patterns of three flowers, three circles and three flower circles. They each form natural triangles around one another, as you can see here:
Stamping in triangles will also help you to evenly distribute your images around your cardstock. Ever start stamping three different images and find that you just have to put two of the same right next to each other? I have--ugh! But I find when I work slowly, stamping just one image at a time, and I use the triangle method I don't end up with this problem!
Hope you find that little tip to be helpful! Let me know. And happy stamping!