The easiest way to stay in a mindful state is to give the mind something to do. In meditation we direct the mind to a single focus, often the breath. This strategy also helps to stay in a mindful state. Try narrating your experience in every moment.
"I breathe in. I breathe out."
"I am breathing."
"I am walking (eating, sitting, writing, etc)"
When the mind begins to wander, simply return to the moment without judgement. Be gentle with yourself. Mindfulness takes practice.