Plan and Prepare
If you are new to underground exploration then consider joining a local caving club and signing up for caving courses (including learning first aid skills). Become proficient before trying the skills for the first time underground. Understand how to respond in case of accident.
Research the trip that you are planning. Is navigation complex, is the route subject to flooding in poor weather, what equipment is required, what personal skills are required,
What are the hazards? Does the route suffer from mine gases or oxygen depletion, is there unstable ground, are their false floors? Is there an emergency escape route in case of collapse?
Equipment
Make sure that you have suitable clothing (including a helmet) and footwear. Make sure that you have a reliable headtorch that will last for the length of the trip, and carry an emergency spare light.
Ensure all equipment is safe and fit for purpose. Check your ropes and personal protective equipment as you pack it.
Always plan for emergencies and take sufficient food, first aid kit, whistle and knife. For SRT trips include a basic rescue kit (pulley, spare karabiners, spare rope and an emergency jammer).
Where there is the potential for mine gases or oxygen depletion then you should carry a calibrated and bump tested gas detector, and know how to interpret the readings.
On the day
Check the weather forecast and consider how the weather over the preceding days may have affected the route.
Always tell a trusted person where you are going, how many of you are going, how long you are planning to be and what time they should call for rescue. Ensure that they know how to call for rescue.
Consider the capabilities of the party members and if they have the fitness and skills to complete the intended route. Check that no one is ill or carrying an injury that might limit their capability.
Make sure that everyone has the correct equipment.
Double check rigging. Before committing to a rope, check that there are suitable knots at both ends.
Pay attention for hazards – loose rocks, false floors, unstable ground, rising water, the condition of anchors being used, rope rub or damage to equipment, signs of fatigue/hypothermia.
Do not be afraid to retreat and return another day if things are not going to plan. Rescue from underground is complex, and in some cases might not be possible.