I have never been real big on collage, so it took me a long time to warm up to it, but many people love collage right from the start. Regardless, it is a fast and easy way to include complex imagery that you may not have the time or ability to create yourself. It can also offer some wonderful stream of consciousness associations that you can offer some insightful surprises.
I don't like rifling through magazines and books when I am ready to create, so I have a folder full of images that I have cut or torn out of old books and magazines or images of my own life that I have printed or copied, often in black and white. Then it is easy for me to simply open the folder and quickly select an image or two without thinking about it too hard. You can then either cut the image out, or tear around the edge to make it blend in easier. But as you can see in this image I didn't even bother with that. I just pasted it in with some acrylic medium and my trusty old credit card.
Then I start painting around it and integrating the background with color. I then use marker or charcoal to continue to draw into it, altering the original image as my imagination sees fit. The end result is often something quite unexpected and offers a rich terrain for my spontaneous writing to flow forth from.