this is such a complicated question , that I paused before answering.
what you like , and dislike , might not be the same thing for someone else. this is important
go to Sweet marias and roam around ;
https://legacy.sweetmarias.com/library/
https://legacy.sweetmarias.com/library/search/espresso/
https://legacy.sweetmarias.com/library/espresso-choosing-the-right-coffee-for-espresso/
the last article is a good one to point out different blends offer different tastes
I use a bottom-less portafilter
the thickness of the stream tells me exactly what my cup is going to taste like
if the stream is too thin , either from too fine a grind , or too much pressure in the tamp
its going to be a very bitter cup.
using the same beans , a very slightly coarser grind , very very slight , and the right tamp will give me a perfect cup
it also took me a long time to realize , as Tom from SM states : espresso is better at a lighter roast than the darker i prefer for drip.
so Id think about the roast you are using , both the bean blend , and the roasting level
and the grind and tamp.
and go from there
a P.S.: with the perfect bean blend // roost level that suits your taste
you can get a Perfect Cup , but you can also get a terribly bitter cup if the density of the coffee puck is too dense
ie Grind + tamping leads to to slow an extraction.
and if the grind is too coarse and the tamp is too light : you get a fast extraction and a very mediocre cup
its less important the gms / puck than the extraction rate for each puck
it takes practice.
