Find out what they like to do, don't involve them in something just because it is easiest for you. Help them to find something, and encourage them. Be honest with your child. It is very difficult to regain trust once it is lost. Most children progress from smoking to drinking to drugs.
Most children first get cigarettes and alcohol from family members.
They take them from what is around the house. If a child lives in a house where a parent is doing drugs, it is very likely that they will start to do drugs too. If you do drugs, how will your child be able to believe you when you tell them drugs are bad. If you drink, do so in moderation. Explain to your child that they will have to make decisions about drinking when they are older, but right now it is not OK for them to drink.