So, I see the difference of i.e. "this sauce is good" and "this is a good sauce", but how do I remember which is which?! I don't see any obvious logic in the differences and I'm going slightly crazy here :)
just think of "הזה" ("this") in "הרוטב הזה טעים" ("this sauce is tasty") as an adjective, and use it just how you would any other normal hebrew adjective. it's almost like you're saying "the this sauce is tasty." at least that's how i remember it!