Factors that often accompany the flow state

Having clear goals about what you want to achieve
Concentration and focus
Participating in an intrinsically rewarding activity
Losing feelings of self-consciousness
Losing track of time passing
Being able to immediately judge your own progress; instant feedback on your performance
Knowing that your skills align with the goals of the task
Feeling control over the situation and the outcome
Lack of awareness of physical needs
Complete focus on the activity itself