To the OP, it doesn't sound like you're really talking about espresso, so these are general guidelines for any coffee process.
darker roast = more bitter (and up to a certain point, also more sweet)
lighter roast = less bitter, more acidic, more coffee origin flavors and aromas
Hotter water = more bitter (and up to a certain point, also more sweet)
Cooler water = less bitter, more acidic
The acceptable range is 90°C to 96°C. For brewed coffee, I like 93°F for the lighter roasted beans I favor. With some natural process beans (often my very favorite) I get the best balance as low as 90°C.
Finer grind (drip) or longer extraction (press pot) = more bitter
Coarser grind (drip) or shorter extraction (press pot) = more sour, weaker development of flavors
Larger dose = heavier body, stronger flavor (if you go too far, subtler flavors will be masked, and it will be hard to know what you're tasting. It might not be obviously too strong).
Lower dose = lighter body, weaker flavor
The acceptable range is around 5% to 7.5% coffee relative to water (consider water to be 100%, so 7% means 7g coffee to 100g water)
I use 6.4% with a press pot.
My advice would be to leave the water temperature and dose (brew ratio) alone in the beginning, and play with grind size. 93°C will be reasonable for any good coffee. As will a 6% brew ratio).
If you're using a press pot, grind size will be coarser, but really doesn't have to be as coarse as some suggest. Somewhere between the coarsest setting people recommend and drip-size works well. 4 minutes total brew time will give good results.
But first make sure the coffee is good. If it's overroasted, it's going to be bitter, and it's going to suck no matter what you do. There will be no way to balance bitterness and sourness or insipidness with it. This describes 90% of the coffee available at stores and everyday coffee shops in the US, so don't assume your coffee's ok just because it cost a lot or is convincingly branded. Coffee roasters should be presumed guilty unless proven otherwise.