You want to avoid oxidized oils and oils with a high Omega-6 : Omega 3 ratio, as these are inflammatory (and reducing inflammation reduces disease incidence). For the most part, seed oils and vegetable oils should be avoided, as well as any oil that has been burned, processed using high heat, or stored improperly.
Fats that are mostly monounsaturated fatty acids (MUFAs) are unquestionably healthy. Those are your fruit oils such as olive or avocado, and nut oils, such as macadamia or walnut. Saturated fats appear to be more or less benign, and fish oils are unquestionably healthy, so long as they are of high quality. There are some additional complexities such as grass-fed butter being a healthier choice than standard butter.
The 80/20 of it is to avoid inflammatory oils, and focus on MUFAs and DHA/EPA.