Filament test pattern
One important thing when playing around with an 3d printer is having a test pattern, which is useful to test if your printer is working. You want a pattern that is quick to print, and interesting to show of to others.
Things
As a 3d printer owner, I know the fun of making my own models. My favorite method of making my own models is using openSCAD, which allows you to make 3d models using just using code, rather than clicking around in a UI.
I have a fair bit of experience in modelling using openSCAD, and I have quite a few functional things using it.