Hi Fredrik,
That’s an excellent question. And you are right the order can matter greatly…
I’ve found some articles by Chris Webb you’ll find interesting. His recommendations, start by removing all unnecessary columns from your tables, especially if you’re doing transformations such as sorts, merges, groupings, pivots or unpivots. And most optimisations the Power Query engine can use only happen on tables – not records or lists – so you should always try to work with tables whenever you can.
Full article and more, start reading here