To "Just Say No" to drugs and alcohol, one must have a reason and that reason must be that there are more interesting activities to choose from. It also helps to have an answer to peers who may offer these substances to you.

Realize that abusing drugs and alcohol may not be fulfilling in the long run, and sometimes leads to devastating events in people's lives, including prison, homelessness, serious medical problems, and even death.
Think about what activities have been more fulfilling than drugs, such as investing in career or bonding with family, your parents.
Examine all fulfilling activities closely. Think about the compliments received from utilizing your skills, the rewards of pursuing an interesting career or how much love you recieve from your family.
Compare the results of your interests to the results (long-term and short) of abusing drugs and alcohol.
Realize that pursuing interests is more fun, cheaper, healthier and EASIER than abusing drugs or alcohol.
Prepare yourself for occasions when friends, peers, or even strangers offer drugs or alcohol to you. By understanding the issues cited above, you should be able to tell the person why you choose to refuse to participate in what they offer.
Try to associate with people who do not use alcohol and drugs, and avoid situations where they will be used and offered to you.
Have a good friend who you can talk to about any situation where you are tempted to experiment. This will help you be accountable, and it should provide you with positive feedback from someone who genuinely cares about you.
Remember that the future is full of hope and promise, and that abusing drugs and alcohol might rob you of those beautiful promises.
Look at the list of successful people who have been destroyed, even killed, by drugs and alcohol. Just because many musicians and friends use them that doesn't make them cool; you must make your own decisions.
Forgive yourself if you feel like you made a mistake by trying drugs or getting drunk in your past. The thing that matters is what lies ahead of you, not what is in your past, especially since the past cannot be changed.

Be aware of your talents, skills and accomplishments so you can think of them when you feel worthless.
Realize that you can create your own "buzz", or happy feelings, by caring about, and building, your future.
Past accomplishments are key. If you succeeded before, you can do it again.
Think about what you enjoy doing the most.
You can never look back at a substance-abusing episode with pride, but you can when recalling how you utilized your skills.
Closely examine what has made you feel valuable in the past, as we don't hurt what we value.

Seek medical and professional advice when stopping all substances, as withdrawing from some drugs (alcohol, pills) can be life-threatening.