I think it's ALWAYS a good idea to start off slowly and get more strict over time because it's easier to stick to. Most people think "well, I'll start off super strict" but they can't maintain it, and so then they go from a kind of thing where times were really bad but then get a bit better, instead of the other way around.
Much better to sway sustainably and make small changes over time, than to go for too much and fail. "She who reaches for the stars, often ends up flat on her face"