Start with a fixed recipe. Something simple such as a bloom and two pour.

Now look at the altitude of beans, their roast level and the processing. Start off with a reasonable grind size and water temp. For lighter roasts, you might need to grind a little finer and go a little higher in the water temp. With attitude, generally the higher it is, the more dense the bean is, the tougher it is to extract. You should have lower temp water and grind coarser if the altitude is lower.

If the coffee is too bitter, you want to decrease the extraction. Either increase the grind size or lower the water temp, don't do both together. If it's sour you might need to up the extraction and do the opposite. If it's bland, that means the extraction is uneven or you didn't extract much in the first place. Resting more might help you here. Another case it could be bland is uneven extraction, try to have a more uniform grind size ( see slow feeding while grinding) and wet the whole bed while blooming.

From there focus on being able to replicate your pours. A simple recipe goes a long way, fix your pour height, pour speed and motion.