First Aid advice given in current U.S. Armed Forces Survival Manual is to bind the limb so as to constrict blood flow and to elevate THE BODY above the limb. This is to slow or stop the venom from reaching the casualties vitals.

Note: THIS IS THE OPPOSITE TREATMENT TO THAT GIVEN TO A SUSPECTED HEART ATTACK VICTIM.

One major problem you have is identifying the snake. Some venom's are blood agents that act as a coagulant. Causes Heart failure. Others are nerve agents. Nerve agents are far and away the most life threatening.

All that assumes that the bite is to an extremity. If it is to the body then unless you have a supply of the antivenin to hand it is quite likely that the victim will die.

Devices like the Sawyer might help to reduce the dosage from the bite but that depends on time since bit, type of venom etc.