Begin by making sure firearm is unloaded.

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You will need a vise block fixture or AR-15 action rod to hold the upper receiver securely in a vice.
 

Fixture the upper receiver in the vise block and clamp it securely into a vice.
 

Remove existing muzzle device, handguard, gas block, barrel nut and barrel.
 

Apply a very small amount of grease to the threads of the upper receiver and the outside of the barrel extension.
 

Insert barrel extension into the upper receiver making sure alignment pin inserts into channel.
 

Insert barrel nut onto barrel with the wrench flats facing forward. Screw nut on upper receiver hand tight.

Using a 30mm crows foot type wrench and an adjustable torque wrench, torque barrel nut to 45 ft lbs. 

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Install gas block and gas tube.

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Insert the three clamp screws into the bottom of the handguard clamp and tighten only a few turns.
 

Install the two set crews into the bottom of the handguard and tighten until they are flush with handguard.

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Install handguard over barrel onto the barrel nut making sure the anti-rotational device at the top of the handguard fits onto the upper receiver.
If this does not fit, your upper is not made to mil-spec dimensions and you will need to remove the anti-rotational device and reinstall it backwards, so the two teeth now protrude onto the side of the handguard.
This will allow you to use the handguard on non-mil-spec uppers.

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Align the handguard top rail with the picatinny rail on the upper receiver.
Make sure the handguard is tight against the upper receiver and tighten the three clamp screws to no more than 40 in. lbs.
Tighten the two set screws to no more than 10 in. lbs.

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Install muzzle device.