How do you get your shifters to sync properly?

I've been biking my whole life, but I've never had a bike that shifted properly. Like I've literally bought a bike, and right from the shop, the shifter's clicks don't line up with the gears properly. And then it's a game of going up two clicks and then back down one to get the chain lined up properly.

So how do I get it just right? The bike I have has Shimano twist shifters all the clicks numbered, but the numbers don't line up with the actual gears.

The closest I've gotten it is where it works perfectly when the bike is on the lift, but as soon as there's weight on it, it goes out of sync again.