Pre-teens should be washing their face in the shower in the evening, then applying moisturiser to damp skin. A wet face washer in the morning then light moisturiser/SPF is suitable. Don't expect your pre-teen to remember this at the start. You will need to remind them every time as they are going to take a shower, "Don't forget to wash your face with that cleanser". Then when they get out, "have you put on your moisturiser?" It is essential to nag a little until it becomes habit.
Teenagers that cleanse their face twice per day, with a consistent routine always see better results. It's important though not to judge your teen. Just gently encourage. Products should be chosen according to the type and severity of the skin condition. Try to change pillow slips once or twice per week. Clean any headphones with alcohol wipes and clean make-up brushes every week.
For adults conditions such as rosacea, seborrheic hyperplasia and peri-oral dermatitis are often misdiagnosed as acne. There can be many contributing factors to consider with adult acne. If you attend a clinic and they try to sell you the same "acne skin pack" of products that they sell to teens - then this is a red flag. Before you spend your hard earned money on those products seek a second opinion.