Grilles are the fastest visual upgrade on a BMW - and the most common ordering mistake.
Chassis first, not year
The same generation often spans several chassis. Check your chassis code (e.g. F30 for the 3-series sedan 2011-2019) and only pick parts made for it.
Single or double slats
Single slats stay close to stock; double slats bring the M look. Both fit directly in place of the original.