Quick forewarning, if you have the Mineral Town bachelorettes in your DS game, the game will end if you marry them. But, if you're going for Celia, then no probs.
I have DS Cute but it's the exact same as far as sprites go, so what I did was:
Chop/smash the living hell out of all the available lumber, and once you start unlocking those sprites, assign them to do that for you. If they do it well enough and long enough, the next lumber you chop/smash should unlock more of those sprites.
The same goes for fishing. Also, I know there's some kind of make-money-fast glitch in DS that has to do with assigning the fishing sprites their job in the winter, but I don't know it off the top of my head.
But, this guide is pretty thorough. http://faqs.ign.com/articles/733/733426p1.html