No matter what the leprachaun says don't touch the flowers on the stove. They might look pretty with their blueish orange color but thay can hurt.
Have a friend around when you try anything for the first time. They should be sober also.
Avoid hardcore drugs. Any opiate is bad and highly addictive. Many people have fucked up their lives because of it. Also stuff like valium is bad. Strong prescription drugs shouldn't be fucked with. I know people who have gone into a coma trying to quit valium and have almost died. They were so delirious that they shot holes in their walls. It's like a like 3 day nightmare ending with coma/death usually.
Inhalants are also pretty bad. You can easily die the first time and there is no way to predict what might happen. Inhaling gas fumes is never a good idea. The only exception to this might be nitrous although you're still cutting off oxygen to your brain. Inhalants are almost as dangerous and are alot less predictable than crack or heroin.
Don't be stupid. Pick a place where you won't be bugged/caught. Going to your local Mcdonald's while tripping on acid is bad. The cops won't except "Sorry officer, if i hadn't just smoked that huge bowl this wouldn't have happened." as an excuse.
When you pass 18 getting caught is really bad. Juveniles have the advantage of being able to get off with a fine or community service. After 18 you spend time in jail. No if's, and's or but's. If you want to try drugs, do it before your 18.