If you want to do a practice — such as constantly watching the mind — you should have a strong intention, and make a commitment when you wake up: 'For the rest of this day, I will put into practice being mindful as much as I can.' It is very important that, at the start of the day, we should decide what we wish to happen throughout the day. At the end of the day, look back and check how you did.
This will help you start and end the day in a positive way. If you didn't manage to keep returning to a mindful state, don't worry, try again tomorrow.