[sanddrag]

Essentials:
Learning the software environment, and the various toolbars and panels.
Setting up a project file, and managing your files.
Using all the view tools (rotate, pan, zoom, etc).
2D Sketch tools (line, circle, arc, rectangle, trim, mirror) and sketch constraints (parallel, colinear, tangent, etc).
Extrude, Extrude Cut, Revolve, Revolve Cut, and Hole features (3D).
Fillets, in 2D sketches and 3D features.
Linear and circular patterns, both in 2D sketching and 3D features.
The "Project Geometry" sketch tool, and making parts adaptive/linked
Placing IPT part files into IAM assembly files and properly constraining them (typically "Mate" constraints) and learning where and how to click to get the constraints you want, and getting fast at doing this.
Creating IDW drawing files with proper dimensioning (and tolerancing).

If you can do all of the above, that's 95% of what you'll need.