I live and die by lists personally. I will make a list of things to do before I'm done for the day and I try to knock the list out. But I also have a drop-dead end of the day time. Don't pull an 18 hour day unless you're so deep in the zone you don't realize you've done it!
You sound like my Dad. . .which isn't bad but I've heard it all before. I don't know why I resisted this list making mantra for such a long time, but nevertheless, I gave in a little over a year ago and started making lists my college course work.
But a list in college is different since the assignment is my constraint thus it is much easier to work within because the assignment or project provides the problem and upstream requirements for me. For some reason reading software requirements, doing a mathematical proof, or looking over case diagrams for pre-existing problems puts me on the right train of thought by forcing me to focus on how I'm doing it not on what I'm doing.
I often suffer from the same day-dreaming and building castles in the air problem you described in your OP.
I have found that just writing down all these ideas allows me to focus on something else. I think the reason I constantly think about them is that I'm attempting to remember everything. The act of putting it on paper allows me to rest easy on that front.
I also prefer legal pads to everything else I have found, even electronic. There is just something about pen and paper and being able to cross out or annotate that helps me organize my thoughts. I sound like a luddite saying that, I know, but it's true.
I also spend some time every so often to go through my lists and consolidate or elaborate on items. Many times I'll find the reason I haven't been able to start on something is because it's too broad and ill-defined. Thinking about it and turning that one item into half a dozen more actionable (is that a word?) items helps get me started.
