It's always the same with me - I blame the coffee. About every six months or so I cast around for a nice little puzzle game to play over my lunchtime latte. I usually find something, but for some reason I end up wanting to have a go at something similar myself (which explains why my next upload will be a Sudoku generator
I don't know if it's a good place to start, but I begin by writing the easy bit - something to create a puzzle in its solved state. After that I find that it's not too bad to code up a solver which looks backward - find how to get to the original puzzle from the solution by removing information one piece at a time, while retaining a path to the final answer.
And after THAT of course, it's not too bad to write the clue generator which tells the solver what to do.
And after THAT comes the hardest part of all... thinking of a stupid name and a stupid splash screen