Like a well oiled machine
very well/efficiently run; smoothly running without any problems. Usually said of an organisation or system of work
e.g. I went to my favourite restaurant today for the first time since the Covid lockdown. I was nervous but they had everything in place - social distancing, frequent cleaning, all the staff were wearing masks and washing their hands frequently. It was like a well oiled machine.
The idiom obviously refers to the fact that oiling machinery helps it to run smoothly.
A similar idiom is to say “it was a slick/smooth operation”