Be cooking with gas
Definition 1 of 1
Pro Tip 1/3Colloquial Usage
Used in casual conversation, not in formal or written English. 
After figuring out the controls, I'm cooking with gas in this video game!
Pro Tip 2/3Positive Connotation
Implies enthusiasm about the success or efficiency of an activity. 
With the new software update, my laptop is really cooking with gas!
Pro Tip 3/3American Origin
Rooted in American English, may be less familiar to non-American English speakers. 
She understands the calculus principles now and is cooking with gas.