In Wild World, I painstakingly sold bugs, fish, fruit and items til my loan was finished. Took me around a year or so to do so.
In New Leaf it was different this time around because I had over a million bells earned from here to help pay off my loan so it was much easier to pay off this time around. Plus I didn't need to collect fruit like a mule this time. I had the beetle farming at the island this time to make it much easier.
I got help with bells for upgrades nyehe<3 I still have most all the bells saved and am still working them into my towns theme/design huzzah<<(^_^)> I am also saving on my own through beetle farming haha xD
I also went beetle and shark hunting to pay off my house. But nowadays, I get most of my money from selling villagers (still haven't spent all that I got from Ankha). I'm also thinking about getting into the stalk market.
Mostly fishing + beetle hunting. If you implement the Bell Boom ordinance and go beetle hunting on the island, then you can easily sell more than 400k per day if you start catching early enough.
A combination of beetle farming and fishing for most of my main house, though I did the last debt or two from duped crown money. Also used duped crown money to pay off most of my Alt's houses... the last of which will be paid by all my Villager Trade profits. :v I fall into the habit of duping too easily near the last payments 'cause I got a duper buddy from CF I still play with. Heh.