You don't say which version of the program you're using but, in version 10, if you select several media clips on the timeline at once, you can right-click and select the option to Add Default Transition between them all. (You can also designate any transition as the Default Transition.)
You can also use the Slideshow Creator in the Media panel to apply the Default Transition between any stills you've gathered to create a slideshow from.
And, if you create your slideshow in the Elements Organizer (prior to sending it to Premiere Elements), you can select the option to add random transitions between your slides.
You can learn how to do all of these thing step by step in my books, by the way, if you're interested.