A mistake on any brewing step can seriously degrade the quality of the finished product, and additional effort on any step can improve it. I guess you figured that out and you’re looking for the points in the serial (or it could be “cereal” process) that give the most improvement for the least effort. The more I thought about the question the harder it became to answer.
All of the suggestions given previously sound right and I don’t have the expertise to disagree with any of them. Instead, I’d like to start a summary of the steps so you and others can analyze your system to find the points where you can concentrate your efforts most effectively - for you. There are several threads on this forum and discussions in brewing texts discussing each step in the process, so once you’ve identified the steps you can research ways to improve each of them and focus on that step - or not. My first shot at summarizing the steps is:
Recipe formulation: grain/extract and hop selection
Grind: fine enough to maximize yield without a stuck mash/sparge.
Water analysis and modification
Mashing methods and mash temp control
Sparging methods and temps
Boiling methods and duration
Finished wort filtering and clearing
Yeast preparation and pitching
Fermentation temperature(s), duration, and secondary (or not)
Racking off yeast
Carbonation and Packaging
Conditioning and aging
Relax, Don’t Worry! Have A Home Brew!
I almost forgot Sanitation! Then I inserted it at the points where it must be considered.
What additional steps need to be considered?