If you want a quick reference for brew ratios, see our quick brew guide here, but if you're looking to dig a little deeper into things, let's run through some brew theory.
Rather than get too far into specifics for each brew method, it's important to understand the theory behind the coffee and its flavors. At its most basic level, coffee is just tiny bits of coffee dissolving into water (brewed coffee is 95% water). Beyond this though, there are two important things to consider when trying to perfect your cup: 1) hot water dissolves things more effectively than cold, and 2) the flavors of coffee extract in a predictable way.
Extraction Order
It's this second point that much of coffee brewing theory hinges on. As you try to dial in grinds, ratios, water temperatures, brew methods, just remember this order:
1) Acidity
2) Sweetness
3) Bitterness
As the water chips away at the grounds, acidic flavors dominant the flavor profile at the beginning of the brew, then sweet flavors start to shine, and lastly the bitter components. You can even try this yourself by splitting your brew into three roughly equal parts. If you use a pour over and scale, start brewing normally and just fill three separate mugs equally by weight as the brew progresses. If you have a drip machine, let each third brew into a separate mug and taste them side by side, maybe timing how long that machine typically takes and dividing by three. You'll be shocked how much each of the flavors dominates that specific cup. When you're done tasting them individually, mix them together to get the flavorful cup you were expecting.
[Quick note- don't be put off by bitter and acidic. While these flavors often have a negative connotation, they play a major role in many of the things we love- think apples or oranges for acidity and cocoa, or mint for bitters. Take away the acidity or bitterness from your coffee and you're left with a pretty lackluster brew.]
Time to Adjust
Once you're armed with this knowledge, you can tweak your routine to compensate in one direction or the other. Since we know coffee is just water interacting with ground coffee beans, we can make a good guess that a really bitter cup means the water extracted more flavor, and if we make a super acidic cup, we can guess that less flavor was extracted. The easiest levers to pull to alter extraction are going to be 1) grind size and 2) dosage.
For grind size, smaller particles create more surface area for the water to interact with. If everything else is equal that means a smaller grind size increases extraction and might tilt the flavor balance towards bitter. The opposite is true with larger particles decreasing extraction and tilting the balance back towards acidity. The same logic applies to dosage, but not necessarily in the way you might think.
Even though increasing the amount of ground coffee might seem like it would increase the opportunity for extraction, if water and brew method are held equal, it might actually decrease the amount of interaction each bean is able to have with the water as a whole and create a more acidic cup instead. While a smaller grind size increases the opportunity to extract the flavors within a bean, adding additional coffee creates competition for the water's attention. If we decrease the dosage, this might result in too few coffee beans interacting with the water, which could create a more bitter cup.
Optimizing for Flavor vs. Strength
It's worth noting that this specific discussion is dealing with the flavors, not the strength. Strength can mean many things to many people so we won't spend too much time on the semantics of it, but this is an important distinction to make. To make it simple, think of strength as the dilution and flavor as the content. The goal of every cup of coffee should be to produce one that first has the flavor content and profile you most prefer, and then ensure it has the desired strength.
Seeking strength by changing flavor is a common mistake. We might say we like "light" or "mild" coffee and decrease the dosage to achieve this. While seemingly intuitive, what we often end up doing in this situation (depending on the specifics of that brew method and coffee bean), is making a more bitter cup that is more watered down. In reality, if we want a lighter cup, we should focus on getting the flavor mixture that we prefer first, and then add additional water. Seeking a "bolder" cup requires a little more tweaking since we can't remove water from a brewed cup, but the answer here might mean pulling both levers at the same time - dosage and grind size.
Don't get me wrong- getting the perfect cup isn't always simple, and it's not uncommon to require changing more than one variable. However, these principles give us a starting point for how to adjust our brew methods (preferably one variable at a time) until we land at the sweet spot of flavor we're looking for. Every bean might be slightly different and every brew method possesses its own quirks, but before we get lost in the mountain of information that is coffee brewing (water, brewer type, origin, process, roast level, temperature to name a few), it's good to start with an understanding of how we affect these basic flavors.