Paper & Pencil
The most valuable thing you can have in front of you when taking instruction from air traffic control is a piece of paper (or a notebook) and a pencil or pen. You can then write down instructions as they are read to you, repeat them back, and have them for future reference.
If you want to listen to and talk to others in flight, you will need to join the VirtualFlight.Online Discord server. Discord is an application you can run alongside Microsoft Flight Simulator, and provides excellent live voice-chat and screen-sharing facilities for free. Discord server membership is by invitation - visit bit.ly/virtualflightonlinediscord to get a free invite.
Configure "Push to Talk" in Discord
The ATC voice channel in Discord will enforce "push to talk" - meaning you must have a key or button mapped, which must be pushed down while talking. Push to talk results in only intended messages being communicated, and keeps the airwaves clear for other pilots.
To configure push-to-talk in Discord:
Click the cog icon next to your name at the bottom left of Discord
Click "Voice and Video" in the left margin (about half-way down)
Change the input mode to "Push to Talk", and select a key or button in the "Shortcut" box that appears.
After configuring, you will then need to hold down that key or button to talk. This helps keep channels clear, and prevents any untoward communication being broadcast too.
In order for Air Traffic Control to see you on radar, you will need to run a small Windows application called "Transmitter". Transmitter broadcasts your position from Microsoft Flight Simulator, such that ATC can display your position on a live map. Within the Transmitter application you can set the callsign you will be seen as by ATC.
Choose a Callsign
Within Discord, it is helpful if you change your username to reflect your callsign (so ATC know who is talking). To choose an appropriate callsign, you like with to read our guide about callsigns.
To change your name in Discord:
Click on the Server Name at the top left of Discord
Click on "Edit Server Profile"
Change your display name for the VirtualFlight.Online discord server to your callsign, followed by your name (e.g. G-JBEK Jonathan)
You can use your VirtualFlight.Online callsign if you wish - e.g. VFL0100 Jonathan (read as "Virtual 100").
Nice to Haves
LittleNavMap is a free flight planning and navigation application that runs alongside, and integrates with Flight Simulator. While you don't need a live map if using ATC, it serves as a great catch-all if you're not sure where you are.
With it you can view airfields, waypoints, and VOR stations on a map that can also display the live position of your aircraft, and those of anybody running the Transmitter application (some configuration required).
Chartfox provides free downloadable charts for many airports around the world (especially for the USA) - which are invaluable when communicating with ATC to both navigate around airports on the ground, and while flying circuits.
If you can afford a Navigraph subscription, while not essential it provides up-to-date sector and airport charts for the entire world, with a wonderful application to bring them up while in-flight with your aircraft superimposed on the printable charts. Many of the aircraft in Flight Simulator also integrate with Navigraph - allowing charts to be viewed in tablets and glass cockpit displays.