This applies to automatic drip coffee makers. If you fail to meet the criteria of a level, you are at the prior level, therefore muddy, grind-y coffee, no matter if you do everything else, is Level -1 (NEGATIVE ONE) in my opinion. Also note, this is a method I use, and is my opinion, it may be wrong, but I don't care.
Level 0: No grinds, don't mix with old coffee.
Keep the grinds out. Paper filters take out acidity (which may be good depending on your digestive system) but it also takes out some of the flavor. I have also heard (although not verified) that it can take out some of the beneficial properties of coffee as well. I prefer gold, re-usable filters. Whichever you choose, just keep the grinds out.
I have also seen people take the remainder of one pot and put in another, if you do this, you are at level -2 (NEGATIVE TWO) (if this is done continuously, the coffee will become more burnt particle laden and may end up becoming some sort of carcinogen, that is my hypothesis) .
Level 1: Good coffee beans, keep fresh, don't freeze.
Get good coffee beans and grind whole beans close to brewing time. Do research on what is good and find a good roaster that delivers freshly roasted beans. If you have never had good coffee before, you will be surprised that you don't need nuts or flavors added, different types of beans or even the same types of beans from different places have very unique flavors. Beans roasted more than 7-14 days ago are stale (although if you have beans that were roasted 14 days, you can barely meet this level). Anything in a plastic or metal can that is already ground, is beyond stale.
Freezing in your freezer is not freeze drying, I don't care what people think. You will cause it to attract moisture and that isn't good. I don't believe it will slow down the staleness process so I believe it is pointless.
Level 2: Correct grind and amount.
The coarser the better. However, too coarse for the heat will yield under extraction. Too fine will definitely cause over-extraction. Automatic drip coffee makers use a slow brewing process. Making it finer will not make it stronger, it will make the coffee more bitter as it extracts more of the bean that tastes bitter. If you want stronger coffee, use more beans, not a finer grind. If your coffee maker adheres to what is mentioned in a higher level, you can make it with chunks. The chunkier it is, more beans will be required. Since caffeine is mostly near the surface, if you use more beans, you will get more caffeine (even for decaf, decaf is not 100% non-caffeinated). Getting a grind to your taste and coffee maker will take some experimentation.
Level 3: Correct Brewing Temperature
Ideally, you want a coffee maker that gets as close to 190 degrees F. This means it is very hot (so you better protect yourself from burns). Yes, coffee is supposed to be hot when freshly brewed and hot enough to cause serious or even deadly burns, unlike what our legal system seems to think. You have been warned, don't blame me. You may need to research on units that can get to this temperature. It is rare that home units under $200 can, but some have said they can. The one I have does get to 190 and didn't cost over $200 but isn't made anymore so no need to say what it is.
Level 4: Don't burn it!
Ideally, don't keep coffee on a coffee warmer, keep it in thermos or a thermos carafe. If you have to use a warmer, your warmer should barely keep it warm and cut off (or you cut it off) before it starts cooking the coffee. The lower the level the coffee in the pot that is on a warmer the more likely the coffee will be burning.
if you have made it to level 4, your coffee is now drinkable.
Level 5: Roast your own beans (or get beans that was roasted 24-72 hrs ago)
There are a lot of options, but even an inexpensive air roaster is better than nothing. I prefer to roast to just 2nd pop but getting past 1st pop is fine. Roasting is a large enough topic for me to dedicate a page to, and likely, I will soon. So, for now, you will need to research this on your own. I will warn that coffee roasting produces a lot of nasty smelling smoke; you will want to do it outside or under a killer exhaust fan (to maintain temperature, roasting outside in cold weather isn't a good option). The smoke issue alone may mean that home-roasting isn't for you. So you may want someone else to roast for you. It takes around 24 hours for carbon dioxide to release from the beans, so too young will make it bitter (the amount and true length of time can vary up to 48 hours depending on the bean and roast). Although too young is better than stale. Meeting this level will bring you from drinkable to good coffee.