This document is by no means complete, and should by no means be refered to as an absolute authority on the gameplay of Doom.
Contents
Controls
Before you start to play, visit the controls section of the options menu to change your controls to resemble a more modern control scheme. With a few changes, you can be playing Doom just like all your other games, with a keyboard and mouse.
Movement
In Doom, there are several 'bugs' in regular movement that have over time been come to be known as features of the Doom engine.
Straferunning
By pressing Forward and Strafe Left or Strafe Right at the same time, you move faster than you would normally by just running forward. This is basic movement, and once practiced almost becomes second nature.
SR50
By straferunning, and at the same time pressing a button on your mouse to enable mouse strafing and moving your mouse in the same direction as your straferun, you can move even faster. While in SR50, however, you can not turn around, so you sacrifice aim for mobility. This is a more advanced manuver, and is harder to control, but it is useful at times.
Backwards Movement
It's use is limited, but in Doom moving backwards is actually faster than moving forwards. Straferunning backwards, as you can imagine, is proportionally faster.
Wallrun
If you straferun at a certain angle close to a completely flat wall going from north to south, or from east to west, you actually gain even more speed. There is a server setting that allows wallrunning against walls in all cardinal directions, but by default, wallruns are only one way.
Weapons
Weapons in Doom are differently balanced than in most other games.
Super Shotgun
This is the weapon that you will most likely use often. They are usually plentiful on any given map, and an accurate shot can kill an opponent in one hit, but it takes a second or two to reload, and is inaccurate past a few player lengths.
Chaingun
This weapon is most useful at long range, or to chase down a fast moving player. It has the distinctive ability to constantly disorient an opponent from the near constant amount of redscreen buildup it gives the other player, which can affect his or her aim. The first couple shots out of the chaingun are the most accurate, while subsquent shots are less so, therefore to maintain accuracy with the chaingun one must tap the fire button instead of hold it.
Rocket Launcher
This weapon is useful as it is highly damaging to other players, and has a respectable amount of splash damage. However, unlike rocket launchers in modern games, the rockets this weapon fires are slow, so slow that a straferunning player can actually outrun their own rocket given enough space. Useful in the same way a grenade is in a modern game, to flush opponents out.
Plasma Rifle
A very powerful continuous stream of damage, being hit with more than a few of these balls of pain can be a painful experience. However, although faster than rockets, it is still possible to dodge plasma, especially in areas where there are a lot of obstacles. Therefore, use this weapon as if you were watering a garden, for lack of a better expression.
BFG 9000
This weapon is often criticized for being overpowered, but in a 1on1 game this weapon is considered balanced. For a full explination on how the BFG works, please read The BFG FAQ. Once you learn how this weapon works, it is remarkably easy to dodge in a 1on1 fight, or if you know it's coming.