yes you should "stretch the cable". Not hard to do just hook to a tree and spool all but about 5 loops off the drum. Back up till the cable is snug, You can sit in the drivers seat with it running and winch your self to the tree, while pressing on the brakes "not enofe pressure to lock them up or drag them". better to do off pavement but can be done on pavement also.. just hook to something "another vehicle,pole or tree" something that wont move if you hook to a car set the e-brake and chalk the tires so not to drag it. then just pull your self to it. again using the brakes to put tension on the line.
It is best to stretch your winch line before you accually need to use the winch.
Also remember safty.... dont let anyone stand between the vehicle and what it is being winched to. Get something with some weight to it to drape over the winch line when you are winching ( helps if the cable snaps/helps keep it from flying back at you!).
And some leather gloves = even thought the cable is new it can have burr's in it.
Congrates on the new toy and be safe.