The best advice I can give is that you're not going to want to use full power very often. I find that food tastes much better if you cook it for longer at 60 or 70% power then if you blast it quickly at 100%. This is especially true for proteins like chicken. I guess this allows for slightly slower, more even heating without destroying all the water in the food. The extra minute or two of time is worth the huge difference in the final texture.
I find that pretty much any vegetable or rice-based dish will reheat "ok" in the microwave, because of the nature of the microwave itself, which works very well for steaming. When reheating stuff like this, throw a tsp or Tbsp of water in the container, and place a lid on it (but do not seal the lid, you want it vented slightly). Again, stick with less than full-power.
I know someone who swears by boiling a glass of water in the microwave first to fill it with moist, warm air. Supposedly it helps with evenness and faster cooking, and reduces drying out the food; I don't know if I buy it but thought I'd mention it so you and the community can comment/decide. I understand the idea, but feel like you'd lose so much of that just opening the door to swap the water for your food. If you do go this route, it's very important that you understand superheating water, which is dangerous. Don't try to boil water in the microwave without reading that link.
If you're adventurous, there's a line of Corningware Microwave Browning products (scroll about halfway down the page where it mentions browning) - I was given one a half a year ago and was surprised at how well it works. There's a lining of microwave-safe metal (I believe tin oxide) inside the bottom of the casserole/skillet, and you heat the casserole by itself for a minute or two first which gets that blazing hot. When you drop food on it, it actually sizzles, so now you're using a combination of normal microwave cooking and direct, skillet-like heat. I've had a lot of good luck reheating things like pork chops and keeping/adding a crust to them.
Also, there's a book, Microwave Cooking For One, and an accompanying website, that are both supposed to be really useful. I don't own the book but have heard from friends who do own it that you can learn a lot about general microwave use from it - even if you don't plan on cooking from "scratch" and are just reheating leftovers.
All that said, I completely agree with Jefromi's comment. 90% of the food I reheat is reheated in the toaster oven, either preheated like a regular oven, or under the broiler depending on what the food is. You might take an extra 5 or even 15 minutes to reheat this way, but the difference is unbelievable, and the convenience is still the same - I just put whatever I want to reheat into a casserole dish and throw it in, sometimes covered, sometimes not. So, cleanup still only involves one dish, and you can eat directly out of it (though it will be very hot, so be careful!) Once you get into the habit of using the toaster oven, you'll find a way to make up for the small amount of extra time - for example I often I empty the drainboard while it preheats, and wash dishes or something similar while the food heats up.
Microwaves in general provide all-around, not too powerful heat. Very roughly, this means it's kinda like cooking on a low-powered stove, except the heat comes from all directions, not just below. (And depending on the microwave, it might heat a good bit less from below.) The things that work are therefore the things that work with relatively gentle, constant, extended heating. This translates approximately into the following traditional cooking methods:
Steaming. If there's not a whole lot of liquid, and there's some empty space for steam to move around in, this is what you'll get. For example, a covered bowl of vegetables (maybe with a little extra water), or even fish on a plate covered with plastic wrap, will come out about like if you steamed it.
Heating, simmering, boiling. If you've got a more substantial mass of food, you'll get something on the continuum between these three, depending on how much of it there is, what power you set your microwave to, and how long you cook it. This means you can do anything from melting butter (carefully) to cooking oatmeal to boiling noodles. (And along with that, you get the canonical use: reheating food.)
Dehydrating. This is a bit of a corner case, but if there's relatively little water in something to begin with, and it can escape easily, the heating will dry the food out substantially - this allows things like dehydrating herbs or even microwave jerky.
And the things you can't do? Anything that requires high heat, especially dry heat, anything where you'd expect the food to brown or get crispy. Roasting, broiling, pan-frying, and so on - the heat from the microwave just isn't going to accomplish it. And on top of this, anything where the cooking time really matters is a bad idea. Even if the microwave might eventually get it hot enough, it's going to take a bit to get there, so if you're looking to quickly cook something in an already hot pan then take it out, it's not going to work. Yes, there are complex ways to work around some of this (for example the herb-frying Brendan mentioned) but as far as what's straightforward to do, you'll want to avoid all these things; they're easier to do the normal way.
Best Answer
No, it won't change the aroma compared to conventional heating.
Generally, heating does change aroma. But it changes in the same way in conventional heating and in microwave heating (given that you heat to the same internal temperature, which can be very different time and power settings for different types of heating devices).
What microwaves change is texture. That's why the microwave is considered "a horrible thing" among chefs. You can't bake doughs or batters in it, and other things like vegetables can also suffer. Then there is the problem with uneven heating. None of these factors matter with liquids. You can warm milk, wine, whatever, in the microwave, without fearing a taste change.