First off, if you or a companion receive a snakebite, do not panic! The more excited you get the faster your blood will start to pump, and the faster the venom will spread through out your body, if it's present. Not all snakes are poisonous, so this should be the first thing that you should determine, and not all poisonous snake eject venom each time they bite. Approximately one quarter of all venomous snakebites are without venom. One way is if you can identify the snake that bit you, with over 2000 species world wide, this isn't always that easy. The other way of telling if the snake is poisonous is by the teeth marks, venomous snakes have fangs that they inject the venom with, so there should be distinctive puncture marks where the bite is. Any snakebite should be treated as soon as possible due to bacteria present in the snakes mouth.
The pit vipers found in North America like, rattlesnakes, cottonmouth and copperheads have front fangs that fold inside of their mouth and are only used to immobilize their prey, whereas the coral snake has shorter fixed fangs and tends to latch onto their prey in order to inject their venom. The pit vipers have arrow shaped heads making their heads much bigger than their neck, while the coral snake have colored bands on them, like the folk rhymes says "Red & yellow, kill a fellow" referring to the coral snakes poisonous venom.
How you treat a snakebite is going to be based on where you are and if medical attention is readily available or not. The experts claim that you should not cut into the wound and try and suck the venom out, but if your hours away from any medical facilities, you're going to do what ever you can to extract as much of the poison as possible.
Here again the experts say not to use a tourniquet on a snake bite, but if a person was bitten by a eastern diamondback rattlesnake that usually injects enough venom to kill 6 humans, what would you do if you were hours away from medical attention? This is where your going to have to make a judgement call, is it better to lose a limb or lose the persons life, because putting a tourniquet on and cutting off the blood supply to that part of the limb would definitely result in amputation.
Let's use the calf of your leg for an example, put a constricting device above where the puncture wound is, you would then make a small incision across the puncture wound and no deeper than the second layer of skin, cutting too deep would expose the capillaries veins and allowing the venom a direct path into the blood stream and to the heart. If you had a mechanical suction, of course you would use that, but if not, you would start sucking the venomous blood out of the puncture wound. (make sure you do not have any open sores inside of your mouth, as now you would be transferring the venom directly into your own blood stream). Once you suck the venomous blood out of the wound, spit it out immediately and rinse your mouth with water before resuming any further sucking. It's impossible to get it all out, but you'll get some, maybe 25% or so. Always try to keep the wound lower than the heart, (this would be hard to do if the wound was on the face or neck,) restrict movement by putting a splint on the leg.
If the victim is hours away from medical attention, prepare to treat them for shock, prop the victim up so as the heart is higher then the wound, once stabilized, remove rings, watches or bracelets, and keep the victim as warm as you possibly can. Keep the wound clean and do not break open any blisters that form around the bite area.
Do not give them any pain medication, alcohol or tobacco products. After treatment of the victim, wash your hands thoroughly just in case there is any traces of venom on them.
Never apply cold compresses to a snakebite. If you're still in charge of the victim after 24 hours, you can start using heat to help prevent the spread of infection, giving the victim plenty of fluids and at all times keeping the wound clean.
Depending on the snake, the venom can contain poison that attacks the nervous system and the blood circulation. The combination of these poisons can cause a lot of dead tissue and blood cells, also attacking the nerve system that can lead to paralysis, lung and heart failure.
In North America the rattlesnake is considered the most dangerous, then the cottonmouth, then the copperhead and finally the coral in terms of toxicity of the venom.
The pit vipers are the most painful and can cause massive tissue damage in the area of the snakebite. The bite from a coral snake can be delayed for up to 12 hours after the bite, making this difficult to treat if the symptoms don't appear for a long time.