How to properly compare coffees

Before we begin, this is the best way in my opinion, because it allows you to be completely neutral in cupping, the art of tasting coffee. Some other methods exist, like using the aeropress, ... but i tend to disagree with those. As far as I am concerned, this is the better way.
Let's get started with the basics, rule number 1, you need a friend to help out with this!
Ok, in a more practical way, first off you need all the coffees you wish to compare, then you need a friend to help you make them.
but not just make them, they need to be prepared in a specific way to really be able to grasp the true character of the coffee.

First step!
Let your friend pour a little ground coffee, I'd say around 8 grams, into a plain cup. Repeat that for all the coffees you got on the table. Write down the scores, which smelled the best, what the impressions are, ... His sole mission in this round of tasting is basically prevent you from knowing which coffee is in which cup. If you don't know, you don't automatically start favouring one or the other !

Second step!
pour hot water into the cup, all the way to the top, this will form a crust on top of the cup, this is how it is supposed to be. But the trick is to wait at least half a minute, this allows the hot water to really suck in the flavours of the coffee, resulting in more clear results for your test. The subtle nuances found in some coffees will come out much more easily this way.
if you want the test to be as accurate as possible, measure down the temperature and the amount of water. The amount of water is the more important one here! You should do your best and make sure the same amount is added to each cup, as not to influence a taste.
More water can make coffees less flavourful, sometimes it will improve things, this is under the condition of minimal changes. Water amounts are like bean grinders, they can influence the experience!

Third step!
Take a big spoon. Get your nose ready and break the crust on top of the cup of coffee. Start smelling! After you finish one cup, make sure to clean your spoon, the trick here is to avoid "cross contamination" of flavours.
Remember to write down your new findings, this just makes it easier to compare afterwards.

Fourth step!
After the smelling test, remove the crust and the tasting begins! The first part is easy, just use a clean spoon to remove the crust, the tasting itself is the final part.
Slurping is the keyword here. As loudly as possible even. Sounds crazy, but there is a reason behind this silly behaviour!
When you slurp, you take air into your mouth, this allows for the scent to move around in your mouth, increasing the sensations you will experience!

Once you compare notes on all coffees, your helping friend can tell you which is which! You can be surprised by the outcome or not at all. Last time I tried this way, I ended up labelling the Brazilian Yellow Bourbon as my favourite of 5 coffees, to my surprise, I generally am no big fan of the Brazilian beans myself :)