There’s a lot we haven’t covered here; here are some suggestions for what to learn next.
- Boolean modifier, especially useful for “drilling” holes in meshes
- Mirror modifier, useful for modeling symmetrical objects – you only have to work on one side and the other side is updated automatically.
- Solidify modifier, useful for saving material (and money) by hollowing out large models
- Advanced selection, for all sorts of useful ways to select exactly the vertices you want.
- Vertex painting, for prints from services that support multiple colors.
If there’s a single resource I could recommend specifically for 3D printing it’s the tips for modeling in Blender for 3D printing, from Sculpteo.
For further learning, there are many resources including:
Google for “Blender Cheatsheet”; here are some direct links to get you started:
from simple beaker clamp
(public domain license) on the NIH Print Exchange