Great tips in this article! Some additional notes I thought of:

(1) This is because Any() stops after checking for one element, whereas Count() will enumerate the collection.

(3) This is made easier when working with .NET 6 (and maybe some other versions) as the compiler will highlight possible unexpected nulls as warnings.

(5) Highly recommended, as this makes writing unit tests much easier too.

(6) Can be difficult sometimes. I feel that it’s ok to go above 3 for private methods. For a public API, think about combining the parameters into objects or structs where sensible. E.g. instead of having 3 parameters for x, y, and z co-ordinates, consider creating/using a Point to group them together.

(8) Highly recommended. Goes in line with Interface Segregation of SOLID principles.