I never really pursued a "project" although I can say that when I begun taking photography seriously again I had a couple in mind.
A "project" for me is something in the back of my mind. It doesn't necessarily drive my photographic day, but it can somehow skew my choices because it's in the back of my mind.
Let's say you have a project, "People working in my town". As soon as you begin getting out to add some work to the "project", you find a very interesting light on a certain architecture. In that case, you forget about the project and only chase that interesting picture. From time to time you might find that your body or work might, in the future, originate a good series with a common theme: "People working in my town", and "Architecture of my province". But you go on exploring all other interesting possibility which you find around you, keeping somehow in mind the "projects" but never letting them driving you away from the photographic occasion of the moment. That's the way I see it.
Circumstances dictate my subjects and "projects" can be distilled later on tracing "threads" in the skein of the work. Those threads can emerge from themselves, without an initial planning, but once you see that there is an interesting body of work on a certain subject, you might make a mental note about how and what would complete the collection.
Following too closely a "road map" - unless you work in a studio - would lead to let's say chase good landscapes when the light is bad and miss let's say street photography occasions because you weren't paying attention.
My general subject is somehow restricted (architectural elements, urban landscape) but somehow also very large. I could restrict myself to some subjects, e.g. "baroque details", "clocks", "high contrast on fašades", "carriage doors", "courtyards" etc. but I would be assured that when I go chasing baroque details my eye would fall on everything else.