There are some fairly good instructions out there, but please keep in mind that these instructions won't necessarily help you. Warning: don't expect your boot laces to work; better to use a leash or rope if possible.
The only sure thing is to avoid an area where there might be body-gripping traps (or other lethal traps or snares). It doesn't matter whether you think anyone would set lethal traps there; all that matters is that they can and they do. They can legally set them where they do kill people's dogs.Even the best instructions are not sufficient without practice on an actual, full-strength trap. But of course, no simulation will be the same (and most simulations will not be as difficult) as a real-life situation.
Unfortunately for dog owners, body-tripping traps (and other lethal traps and snares) are designed to kill quickly. A dog may be mortally wounded by the initial blow of a body-gripping trap on the throat and spine. That's what's called a "clean kill."