I start with my basic no turret drone in the image below.
Add a free hinge wherever you would like your turret, but make sure it has enough room to rotate.
Attach a VTOL thruster to the back of your turret.
Set the target to nearest enemy, and set the mode to inverse.
I set the activate button to left bracket and I'm going to connect that to a switch later.
I don't know what the fallback setting does, so I just set that also to nearest enemy. (someone in the comments told me what it does, so you should actually set fallback to cursor. That way, if there aren't any enemies around, the turret will follow the cursor.)
You can also add a VTOL thruster to the front with the same settings except with the mode on normal; it will stop the turret from moving the entire drone and will also make the turn speed faster.
Since we are using thrusters to turn the turret, you will need fuel to power them.

I add a switch to my drone so I can toggle my turret by pressing E
Add some weapons to destroy things with. Make sure that the rotation is set to fixed.
Now that it is finished, you can ctrl-d the free hinge to copy more turrets to wherever you would like.
This is the first guide I have ever made.
I think it's really helpful.

Compact and light
Turrets can function independently without having to use separate tags
Can still work effectively against multiple enemies at once
Energy inefficient, Uses both fuel and energy
Precise weapons with slow attack speed don't work very well *cough*snipers
Recoil can become an issue

I find that turrets work best on the back of the drone rather than the front, so the drone can fly away while shooting enemies. If your drone is fast enough, the enemies' weapons won't be able to reach you while your weapons can.
These turrets seem to work best with blasters and shotguns because of the low accuracy and high attack speed.

The flip direction key can allow you to make some unique designs for your turrets.
Here I have used it along with a few logic parts to be able to switch between plasma and cryogenic ammunition. Although this uses multiple inputs, sacrificing the simplicity of the design, it is still almost as compact as the original.