Try restarting your iOS Device by holding down the power button until it allows you "slide to power off". Then turn it back on. Then go to "App Store" again on your iOS Device and try to download it again. You will probably have to click "buy" again - but you will not be charged twice. Then leave it on your desk and wait patiently whilst it downloads - do not run any other applications or touch the side of the iOS Device at all. Try to get as close to the WiFi signal as you can when you try this.
Or try downloading it through iTunes. Open iTunes and click the "iTunes store" link (left hand side). Then click on "App Store" at the top. Do a search for "Comic Life". Next to the Comic Life icon and underneath the description, you should see a "download" button. Please click this button and Comic Life will download in iTunes. Then connect the iOS Device to iTunes and move the app (from "Apps" under "Library" over to the iOS Device (under "Devices").
If you continue to have issues, please contact Apple iTunes Support.