If you already run Octoprint, you might find it a hassle to slice in separate software and then upload the gcode to the pi.
In this guide, I take you step by step through setting up the pre-installed CuraEngine, installing Slic3rEngine via SSH and Putty, as well as the Full Featured Slicer plugin so you can manipulate your STLs with a GUI.
The slic3r install is not straightforward, so the step by step is down below. Many people will be happy with their current slicing workflow, so this video will act as little more than food for thought. Personally, I will be implementing this setup to make 3D printing easier for my colleagues at work with a Prusa MK3.