Reducing Risks:-

Never use drugs or alcohol alone
Avoid slipping into friendship groups based entirely around the use of drugs/alcohol
Avoid mixing drugs; using 2 or more drugs at the same time increases the chance of you having problems
If you have a heavy night out, give your body a chance to recover, have days when you don't use drugs/alcohol at all
Think about how you would deal with an emergency; if anyone collapses CALL AN AMBULANCE IMMEDIATELY when the ambulance arrives tell the medics what the person has taken and how long ago.  You could save their life!
Make sure your phone is charged and has credit
Never make you way home alone