Before you start actually playing the game, I highly recommend watching the tutorial videos so you have a basic idea of what you're supposed to be doing instead of just blindly rushing in and losing within 1 minute. I'll still go over some of the concepts in the tutorial videos, in case you don't feel like watching them for some reason.

Also, I'm probably not the best player, but I have a fair amount of experience already.

There are three Killers available in the game, though only one is currently available in the beta.
The one available in the beta is known as The Trapper:

He carries a cleaver and can use Bear Traps, which can wound survivors and trap them until they are freed.

The second Killer is The Wraith:

He can become nearly invisible and ambush Survivors.

The third Killer is The Hillbilly, who hasn't been really been revealed yet so I won't put his picture here. He can sprint at Survivors with a Chainsaw.

As the Killer, your job is to prevent the Survivors from escaping by killing all 4 of them. They must activate 5 Generators and open the gate to escape, or find the Hatch which I will elaborate more on later.

You play in a first person perspective with a narrow field of view, which gives you a disadvantage over the Survivors who have a third person camera.

Generators, Bear Traps, and loud noises are shown to you through walls. Use these to help you orient yourself and patrol around the map.

Finally, you cannot be killed. The most a Survivor can do to you is temporarily stun you.

The most important ability you can use to find Survivors is your ability to see loud noises. They appear as a dark red sphere and disappear after a few seconds. When a loud noise occurs, you should quickly head over to investigate it. The person who caused the noise will not be able to move very far from it if you're nearby, so search their general area.

Survivors who run will leave a trail of orange scratches, so keep an eye out for them. They disappear after a few seconds, so their presence means that someone is nearby.

Survivors will hear a distinct heartbeat sound if you are near, and they will hear music if you are very close to them. You are not able to hear these cues yourself, however. Most Survivors will immediately attempt to hide if this happens, so search around if you know they are near.

Survivors can hide in Supply Closets. Checking a Supply Closet takes a few seconds, so don't go around checking every one you stumble upon. They make a distinctive noise when they are opened and closed, so make sure you're listening for it.

Opening a Supply Closet with a Survivor in it will cause you to automatically pick them up.

A strategy some Survivors use is to hide in a Supply Closet after they have made a loud noise. Ensure that you check any nearby ones whenever this happens.

When you have located a Survivor, the first thing they'll probably start doing is running. Your narrow field of view prevents you from reliably chasing multiple people, so focus on one.

You move faster than the Survivors can run, but they are able to vault over objects faster than you can. Going around an obstacle is generally faster than vaulting over, but there are some scenarios where you can't.

Survivors can drop a pallet of wood in front of you, which can slow down your chase and even stun you if you're too close when they drop it. They're typically found near crates and walls, so keep an eye out if a Survivor is running towards them. Once a pallet of wood is dropped, you can either destroy it or go around it.
Going around is usually the faster option, but some Survivors may continually vault over the pallet to distract you, forcing you to destroy it.

Sharp turns are your enemy. Survivors making them can quickly disorient you because of your narrow view, so try to keep track of what direction they're running in.

You can follow the scratches and noises they make if they happen to get out of sight. Inexperienced Survivors will likely keep running after you've lost them, so watch out for that.

To down the Survivors, you first need to slash them twice. The first slash will put them into an injured state, where they leave a trail of blood and are generally much more noisy. The second will fully down them, and they will slowly bleed out if you let them. Successful slashes on Survivors will cause you to slow down and wipe the blood off of your weapon, while the Survivor gets a temporary speed boost. Try not to lose sight of them when this happens.

Once they are downed, you must pick them up and find a Hook to impale them on. Survivors can struggle to free themselves while you are carrying them, so try to locate one quickly before they can get away.

If a Survivor is slashed while they are doing something (like vaulting) they will be interrupted and automatically carried.

When hooked, Survivors can either be helped off by another Survivor, or attempt to free themselves as long as their bar is above 50%. The chance of a Survivor freeing themselves is very low however, and attempting to do so drastically decreases the time before they are killed. Once their bar is below 50%, spider-like claws appear from the Hook and attempt to kill them. All they can do at this point is struggle to delay the process or get helped by another Survivor. When the bar is depleted, the Survivor is killed (as expected).

If you are standing near the Hook when a player is freed, you will be temporarily stunned and blinded, giving them a chance to escape.

Survivors with a Toolbox can sabotage your Hooks, rendering them unusable. The only Hooks they cannot sabotage are the Basement Hooks. Try to prevent Survivors from doing so, because they will have a better chance of freeing themselves before you can reach a Hook.

Camping a Hook is not always the optimal strategy. While it can ensure the death of one Survivor, you allow other Survivors who are alive to continue working on generators without any threat.

Although the Survivors only need to activate 5 Generators, there are much more than that on the map. Camping 1 Generator is not an effective strategy because of this.

You cannot see the progress a particular Generator has towards being activated, but you can hear it. A Generator that hasn't been worked on won't make any noise, while one nearing completion will be making alot of it. Take note of ones making noise, because a Survivor may be nearby.

If a Survivor fails a "skill check" when activating a generator, it will make a loud noise. Make your way over there quickly, because they likely didn't move very far away from it.

As the Trapper, your ability is placing Bear Traps. You can only carry 1 at a time, and you can pick up more around the map. While placing a bear trap, it sets up noisily and forces you to look down at the ground, which can give them a chance to get past you.

Bear Traps are fairly noticable, so try to conceal them in the grass. Placing Bear Traps around corners and pallets of wood can also be effective.
A spot that's particularly effective is by the corner on the basement stairs. Most Survivors will move along the wall as they make their way down, and walk right onto it.

Survivors can sabotage your Bear Traps if they spot them, which will take them a few seconds. When sabotaged, the Bear Trap will make a loud noise and will need to be set again.

Survivors who sabotage a Bear Trap using a Toolbox will break it and render it unusable.

You can trigger your own Bear Traps, which will stun you and cause you to drop a Survivor if you're carrying one. Take care not to do that, because it's pretty embarrassing.

Survivors who get caught by your Bear Traps will make a loud noise and be highlighted through walls. Make your way over quickly before they are freed by another Survivor (or free themselves).

Getting caught by a Bear Trap counts as being slashed once for the Survivor. A healthy Survivor will escape a Bear Trap injured, while an injured one will escape in a state of bleed out.

The Hatch is the alternative escape method for Survivors, though it is normally closed. It is randomly placed around the map, whether it be outside or indoors. Opening it requires a Key, which has a rare chance of being found inside of a Chest. It can also automatically open up when there is only one Survivor remaining.

Make sure that you remember where the Hatch is. It makes a distinctive sound when open and can quickly cause you to lose if someone escapes through it. Bear Traps can be used to slow down someone trying to enter the Hatch, as they'll either trigger it or be forced to sabotage them.

When opened with a Key, it only stays open for a limited time. Ensure that other Survivors don't make it through the Hatch as well if this happens.

Hopefully you will put some of this knowledge to good use, and start winning more matches as the Killer.

I suppose Survivors could pick some tips up from this guide also, which means that you might not be winning more matches after all. Whoops.

Good luck, I guess.