/ic/ - Artwork/Critique

Hello /ic/. I was wondering if you guys had any advice for achieving good "work flow". I know I've had those days where I can work non stop for 10 hours and not even realize it. Those days where I'm completely focused and immersed in what I am doing and absolutely nothing can break my focus. I usually produce good pieces of art on those days that I'm typically happy with. The problem is that I haven't had one of those days in a while. I just want to know how you guys enter a state of "flow" and if you could give me advice on how I can also achieve it. Any methods, or tips/tricks would be helpful.