Nose Fatigue & Order
When trying perfumes in a store, the first thing I recommend is not smelling too many fragrances one after another. After a while, your nose starts getting tired and different perfumes can begin to smell similar or harder to understand. Try a few, take your time, and come back to others later if you need to. But if there is one thing even more important than this, it is the order in which you smell the perfumes. The logic is simple: smell them from the most intense fragrances to the least intense ones. This is very important. For example, if you smell Oud Zarian and then smell Torino 21, you will probably understand almost nothing about Torino 21, so make sure you get the order right.
Paper vs. Skin
When trying perfume, the “correct” thing is actually to test it on your skin, but this is not always the most optimal way. The reason is that if you spray every perfume you want to try on your skin, you have to leave some space between each one, so the number of perfumes you can test drops a lot and your nose can get tired more easily. In my opinion, the better way is to spray the perfumes you are curious about on paper, check the opening, give them some time, and then smell the dry-down again. If you do not like one, you can simply throw that strip away. This way, you can try more perfumes and you can also let the people around you smell them, since they can smell the paper too, even after you leave the store. There is one disadvantage compared to testing on skin: you may dislike a fragrance on paper but like it on your skin, and in general fragrances tend to smell better on skin. Even though this is a serious disadvantage, I still prefer starting with paper because it gives you the chance to try more fragrances. One more thing: researching a perfume before going to the store and then trying it there is always a much faster and more efficient way. For example, let's say you do not like fruity scents and the perfume you are curious about is very fruity. In that case, you can try it quickly without spending too much time on it, or you may even decide not to test it at all.
Resetting Your Nose
As for the whole smelling coffee thing, some people say that smelling coffee after trying perfumes for a while helps your nose start picking up different scents again, and some stores even keep coffee beans around for this. Personally, I think it can help a little, but of course it is not something that completely “resets” your nose. The best thing to do is still to leave the store for a while and give your nose some rest.