When to switch from ground to tower frequencies at controlled airports in the US?
While I acknowledge the answer by GdD to not change frequencies until instructed, that is at odds with my experience.

When I call Ground, then request and receive taxi-instructions, I stay with Ground to the runway hold short line.   I've never had Ground give me an explicit instruction to switch to Tower.   

When I start my run-up checks, I switch to Tower (unprompted) to start hearing what is happening in the airspace.  When my run-up is complete, I call Tower with a "ready for takeoff".

I've never had Ground, Tower, or any Instructor tell me differently.  I've never observed another pilot wait for an explicit frequency change instruction from Ground, and I believe that is the way I was taught.



Note: this only applies when you've taxied to the hold-short with Ground.  If Ground tells you to switch earlier, do it.  If you want to switch earlier, request it.