It took me some time to figure out how to organize my code so it fits in with the XNA framework design. Because the game is so small, I did this by building some dummy classes and that I renamed and moved around in the project tree until I had reached an adequate design.
Maybe some people would have used an UML prototyping tool, but I am used to thinking in terms of design and code, so, just like a good chess player, I can see when a design will work out or when it will blow up.
Then I identified the hardest, probably most demotivating task at hand. If you can, I think it’s always good to start there because this is likely the point where you would "postpone" working on the project for the rest of eternity.
The hardest part in this project seemed to be the dynamic construction of the level’s 3D model out of a simple text file that defines the maze using pure ascii characters. You have to create a bullet-proof parser and then somehow build a contiguous vertex array for all the walls, floor plates and holes in pure code.
So day 1 ended with me writing a parser for the textual level file format I have layed out before.