Best way to earn the most coins?

What do y’all think helps make more money to reach 3 stars? Upgrading tip amount or upgrading dish prices? I’m getting through the seafood bistro with everyone pretty much tipping and I’ve upgraded most of the dishes to level one, but I’m still only getting 2 stars on the last 10 levels. I don’t want to waste much more gems on this restaurant, but I like completing restaurants with all 3 stars before moving on to the next🥲