When first learning Fusion 360 from a different CAD background, a constant mistake is to make sketches in the top level of a design, rather than in the component it is driving. Cleaning up this mess later is really difficult.
I'd love to see a little toggle check-mark in the User Preferences that would be called something like, "Component Design Mode". If that option was selected, a warning message would be generated any time the user created a sketch in the top level, rather than inside a component. This would be really helpful to people coming from Inventor, Solidworks, etc.
