The microphone is undoubtably the most important part of your set-up. And it takes a bit of know-how on what microphone to pick. There are various different types of microphones, but for our purposes, we will look at Large Diaphragm Condenser Microphones. They are the standard for recording vocals.
The microphone is very sensitive at the front which makes them great for voice-overs.
The front faced sensitivity will also limit the amount of background noise it picks up (think of cars outside, flat neighbours flushing the toilet).
The microphone I use, the Røde Nt1 A, is one of the quietest microphones out there, which is great if you don't want spend too much time in post production editing out unwanted sounds. (more on that later)
These unwanted natural microphones sounds is called a "noise floor".
The Nt1 A is also one of the most affordable voice-over microphones out there, and you can buy them from around £100.
There are loads of great mics out there, at an affordable price. Just don't bother with microphones that cost say £20. I've tried them and really, they are just toys. If you want to take this seriously, you will need to invest a bit.