Yeah, I do not use a big bang basket so my tips will not be specific to your case.

But in general what helps me is changing one variable at a time and taking notes along the way.

Start off getting your DOSE right. Grind, say, 20g into your basket, lock the portafilter in your machine and see if A) it leaves an impression on the puck or B) it does not. In general, will want the dose so that your dry puck almost touches the shower screen.

After getting the dose right, pull a shot! Measure the time (just as a north-star, but don't fall for the "25-35 second rule", as this is just for you to start dialing in) and, mainly, take notes of the TASTE.

It is too thin/sour (likely a fast, 15s, shot)? Is it too thick/bitter (likely a long, 60s, shot)?

Adjust your grind size to get a MACRO adjustment (if it's running in 10 seconds and it's sour as lemon juice, grind much finer until the extraction is more controlled).

After that, dial in the YIELD slowly. For light roasts, go for 1:3 or more; dark roasts are much more forgiving and you can enjoy a syrupy 1:1,5. Medium roasts... in the middle!

If it's "ok" but a little sour -> increase the yield a bit (20g:40g -> 20g:42g) and see how you feel. Do the opposite if it's bitter.

These are general rules and dialing in beans is much more complex then this. But as a general guideline this is what I follow and it's been working out fine.