book: improve a bit of grammar in Method Syntax chapter

src/doc/trpl/method-syntax.md

@@ -50,9 +50,9 @@ parameter, of which there are three variants: `self`, `&self`, and `&mut self`.
 You can think of this first parameter as being the `x` in `x.foo()`. The three
 variants correspond to the three kinds of thing `x` could be: `self` if it's
 just a value on the stack, `&self` if it's a reference, and `&mut self` if it's
-a mutable reference. We should default to using `&self`, as it's the most
-common, as Rustaceans prefer borrowing over taking ownership, and references 
-over mutable references. Here's an example of all three variants:
+a mutable reference. We should default to using `&self`, as you should prefer
+borrowing over taking ownership, as well as taking immutable references
+over mutable ones. Here's an example of all three variants:
 
 ```rust
 struct Circle {