I am a PowerPoint veteran who only recently started to design presentations in Keynote. Here are some of the little things that were hard to find:
  • Connecting shapes with a line: select both shapes go to the insert menu and select connecting lines
  • Remove an image background: go to the format menu and select instant alpha
  • Edit an image (make it B&W for example): select the image and click the tiny button with the levers (next to the stroke buttons).