If you have the time to devote to shop keeping I say buy em cheap & sell em cheap. That is how I grew so fast. Auctions and games are always helpful & the trading post is always good advertising your shop for free :D

Don't forget to do your dailies if you are looking for quick points: http://www.neomallers.com/freebies I also find the free jobs at the employment agency to be a good way to make points. You can earn up to a few thousand nps at a time in about a minute, 5-6 times a day. I've also heard that playing the world challenges are a good way to make points if you have an hour to commit to it at a time and are good at any of the eligible games. I have yet to try this though. The stock market is one of my favorite places to make profit as well, but you have to be able to spare the points and have patience, because if you end up desperate you stand the chance of pulling out your investments at a loss. (At least that's what happened to me years back when I first tried it and didn't really understand how it worked.) Good luck!