As noted, a 2 person job. 3 is even better.
I always like to get and keep the cable a tightly wound on the drum as possible.
As noted, using the properly sized and rated cable is essential to safety as is using the correct sheer pin and NOT a common bolt, especially a grade 8 bolt.
Always use a strap on trees to avoid damaging and killing them (Tread lightly).
Now, how to keep the cable nice and tight? Most winches have some sort of method of anchoring the end of the cable to the drum, of course your going to want to use this. You will need a minimum of 5 wraps of cable on the drum to provide enough grip between the drum and cable to start any winching operation.
To get your 5 wraps you can use the winch power to turn the drum while you CAREFULLY feed the cable. AT ALL TIMES KEEP YOUR HANDS AT LEAST 3' FROM THE FAIRLEAD while the winch is powered. A second person who 100% understands how to shut down the winch should be at the controls.
Once you have your 5 (0r 6) wraps shut off the winch. To get the cable as tight as possible I attach the end to a stout tree or other heavy non-moving object. Have a driver at the wheel a safety person to shut down the winch and you, the cable feed person.
NOTE: The big danger is that the cable can snag your hand or gloves or clothes and suck your hand into the fairlead and literally wrap your arm around the drum until the force of the event is so great that it can and will rip your arm off of your body. This is generally considered to be pretty painful which usually causes unnecessary screaming and of course there is usually quite a bit of blood loss which always seems to splatter all over everywhere and is a pain to clean up. Overall it is noisy and messy and as a general rule you should strenuously attempt to avoid this exercise.
The "Driver" job is to apply brake pressure to the point that the wheels almost lock and slide but not quite. This will apply as much tension on the cable as your reasonably going to get and will not stress the winch in the least. The driver also keeps the truck pointed straight at the anchor.
NOTE: #1: DO NOT Stretch the cable across a street or driveway!! The cable is impossible for a driver to see and this has caused numerous decapitations. This is again followed by more screaming (Yours) and quite a bit of bloody mess (The innocent driver). This is considered poor form on your part and is absolutely to be avoided.
#2: If this is a new cable once you have the first 5-6 wraps and they are nice and neat on the drum and you begin the wrapping op have the driver apply full brakes and slide the truck just a few inches. This will "preload" the cable and remove all slack within the individual wrappings and strands of the cable. Hold this tension static for a few minutes. After a few minutes start the winch again and allow the truck to move as noted above.
The safety persons ONLY job is to kill the winch at the very first sign that any of your various body parts or clothing come within 2' of the fairlead. This person will not be chatting on the phone, texting, iPod listening or doing anything except paying attention to the space 2-3' in front of the fairlead and will at all times have a hand on the kill switch/lever.
Your job is to make sure that the cable feeds nice and evenly across the drum and as the layers build it remains nice and even. You can do this by standing 3-4 feet in front of the fairlead and applying horizontal pressure to the cable. One easy way to do this is with a snatch block and a 6' nylon strap. Put the snatch block on the cable and attach the strap to the block. Move the snatch block to the 3-4' from the fairlead position and standing on the side you want to keep the cable toward simply lean back while holding onto the strap to keep from falling backward. This is enough to nudge the cable where you want it to go.
The last 15-20' or so it is not so important to keep it super tight since you will be pulling at least that much off the drum for most any winching op. At that point you can unhook from the tree and use the nylon strap on the cable hook and just pull against the cable as your safety man activates the winch and finishes the last few feet.
Pretty simple, keeps you safe and avoids that screaming and bleeding scenario.
After any winching op that I have pulled more than about 50' of cable off I always take the time to find a suitable anchor and pull off however much I used plus another 20 or so feet and spool it back under tension as noted above. This keeps the cable always ready for use at any length and absolutely minimizes damage to the cable from heavily loading it with layers beneath.
Of course to eliminate cable damage if I am going to be really working the winch/cable hard I will use snatch blocks (To double pulling power) and or more distance to allow me to use more cable off the drum so that lower layers are not damaged. This has the additional advantage of giving me the most power from the winch. This is because with every layer of cable the winch power is decreased by something like 15% so the closer to the drum you are, the closer you are to being able to use the actual rating of the winch. I always try to leave at least 1 full layer on the drum to insure that I have sufficient "Traction" between the cable and drum to eliminate cable/drum slippage. (5-6 wraps is the ABSOLUTE MINIMUM)
Since you have asked how to do this I am going to assume your a winch novice (Nothing to be ashamed of, everybody has to start somewhere!) I am going to HIGHLY recommend you read the TM covering winching and recovery operations, (Properly known as, "Vehicle recovery operations"). You will find it attached below.
You might also benefit from the list of gear I mentioned in this thread:
http://www.steelsoldiers.com/deuce/62241-help-need-pulled-out-mud-houston-pasadena-tx-7.html
If you get really bored and want to read some more about rigging, read the rigging manual. (Also attached below).
Lots of very good info in those 2 TM's..
Good luck and safe winching!