The more tasks become part of a routine, the less a child has to think about what to do next. Consistency is the key to making a routine stick. Make a checklist that can be laminated and your child can check off the tasks as they are completed. For younger kids, it may help to make a picture checklist. Getting as much ready the night before (clothes laid out, backpacks put together, lunches made, setting the alarm) can make mornings better. Since children with ADHD are distractible, avoid turning on the television or having computer time in the morning. The struggle to have them turn it off and do what they need to do is not worth a few minutes of respite. Set up a reward system for completing the routine. You can even make a game of it by seeing if your children can beat the clock or beat their best time. Remember that children with ADHD are easily bored so even if a system is working well, the benefits may start to wear off after a few weeks. Have another reward system in mind so that you won't be caught off guard. Positive reward systems work much better than negative consequences so try to use those as much as feasible. Accentuate the good behaviors as much as possible so your child does not feel that he/she is "in trouble" much of the time.
For more ideas, check out these links:
From ADDitude: Teaching Time Management to Children with ADHD
National Initiative for Children's Healthcare Quality: For Parents of Children ADHD