The more unknowns a project has, the more I'm inclined to start on it as soon as possible. An "unknown" is when I don't know how to do something, how long it will take to do, whether I will have to do step 5 because of the result of step 4, etc.
The faster I can take care of the unknowns, the less stressed I am about a project. So, for school and work, I tend to start on something as soon as I can, so I don't have to worry about it. In school, even for the routine homework, my philosophy was, "The sooner I get this done, the more time I will have to do what I want to do" - and so I rushed through my homework, completing it on the bumpy bus ride home, and turning in some horribly written assignments!
If there's no deadline, I tend to wait on a project until I have it all figured out. So, for large home projects (build a patio covering, install an attic door, etc.), I will do nothing for months and then one day I wake up and I have the whole plan in my head, and I work on it every spare moment and will all my energy until it's done.