There are really only three keys to a great cup of coffee and I am going to share them with you here...
1. Coffee must be fresh!
Some coffee brewers promote the freshness of their coffee because it is brewed a few minutes before you get it and then it is poured into the drain when it becomes so-many minutes old. That is commendable but it is only half of the fresh equation - the other side of the fresh coin is that the coffee needs to be roasted fresh. Coffee begins to stale the very moment that it is cooked. It oxidizes from the air just as metal begins to rust. The process of staling coffee is impeded in a variety of ways but stale it still goes. (And the freezer method to keep coffee fresh is little more than a mythical hope). I give coffee 14 days before it goes off, not Cinderella off but off enough that one can tell the difference.
Coffee too easily takes on the flavor of the water that is used to make it with. I once made Michigan Snow Coffee and I also made coffee using good old-fashioned rain water - I don't suggest it without good filtration because it was nasty. Even with the tap water you can tell the difference between filtered and non-filtered--So get yourself a Brita or something like it if for nothing else but your coffee.
And here is the greatest of the three...We've all done it. We get the coffee container out of the freezer and use a spoon to fill the filter with grounds, we stop adding grounds only when we "feel" like there is enough caffeine and from pot-to-pot we wonder why we cannot get it to taste the same. The fix to this is to weigh your coffee (ie. For every ounce of water you need a set amount of grounds to go with it). I use a standard .042oz. (by weight) to 1oz. of water (by volume) for my ratio.
Of course, coffee flavor will always be subjective according to the tastes of the person drinking it. There are a thousand things that factor into the flavor of your coffee (what you ate earlier, the roasting profile of the bean, the origin of the bean, the specific crop that the bean has come from, the blend, the cleanliness of the cup that is used, etc. etc.) but getting these three keys under control are huge and will lead to consistency and a better cup of brew.
For those who are purists: Although I did not include it here there is something that needs to be discussed in another post - The idea of the Single Origin bean. Just as a single-malt scotch is preferable to a blended scotch or how a bottle of wine is known for the specific grape that is used to produce it so also a single-origin coffee bean is preferable to the blended grind. At least that is my position as a coffee snob. ;-)