Sanitation. Water. Fermentation temp. Mash pH (if all grain). Yeast health and pitch rate. Quality ingredients. Have fun.
If you allow microorganisms into your wort they will thank you for such a great environment and reward you by (possibly) ruining your beer. I recommend cleaning all equipment and especially focusing on sanitizing the cold side equipment well. If you like to clean and sanitize, you might be a brewer.
If you don’t use ‘good’ brewing water your beer will suffer. I recommend RO or distilled and use 1 tsp CaCl or gypsum or a combination of the two in an average 5 gal batch to get at least 50 ppm calcium . If you choose to use tap or well water you might need to take additional steps to get ‘good’ brewing water.
Maintaining a steady fermentation temp can help improve your beer. I recommend 55° +/- 3°F for W34/70. Others may recommend higher or lower temps. Regardless of the fermentation temp you choose, control that temp from spikes.
If you are mashing grain to convert starch to sugar, mash pH is considered foundational. Good things happen when mash pH is controlled. 5.3 +/- .1 pH is considered the sweet spot.
The fermentation temp, volume and SG of the wort can all play a factor in pitch rate. I believe it is a rare occasion that one 11 g package of dry yeast is adequate. For a 5 gal batch of 1.036 wort fermented at 55°F, I recommend 21 +/-1 grams of W34/70.
If you use old stale ingredients, a crisp light lager will reveal it. There are no esters or phenols or bold ingredients to mask flavor in such a beer. Buy good stuff.
Regardless of issues during the brewday or outcome: have fun doing it. It’s a hobby. It’s supposed to be time well spent and enjoyed.
*Disclaimer*: Any comment I add is simply the way I brew beer. I am not paid or sponsored by anyone. There are certainly other ways that can be equally effective which other brewers may contribute. This is what I’ve found that works for me using my equipment and processes so I offer this for your consideration. YMMV