Well it depends on what you want/like to do. There are many options out there.
Restocking: Basically you hang around in shops buying things and selling them for profit. If you restock an unbuyable its always usually good for a big profit. This could range from 100k-1mil+ although, those are VERY hard to get and they dont show up often.
Stock Market: Playing the stocks I hear can earn you alot. I've never personally tried to base all my nps on stocks, but I do have 1 or 2 lying around that I check on everyday. Basically you just buy stocks at 15, 16, 17, or 18+ and usually in amts of 1000. You have to be patient and wait for your chosen stocks to rise. Then sell them whenever you feel like you have earned enough profit than from what you had in the beginning. I can't really go more into this subject as I really don't know that much about it. Although, I hear hyperflutterby is a pro at this.
Sniping: Buying things at low prices and reselling them for more profits. Shop wizard sniping and auction sniping are among these types. Just search for random unbuyable items on the shop wiz and refresh until you find one that is buyable. This is hard, and may never occur, although sometimes it rarely does as someone misprices their items in their shop. Auction sniping is harder, as there are many people doing it, and have experience. I can't help you much in this area. I did it when I was saving for a lab map and getting certain pieces, but now I am not. Matt (the mod) I think was the person who was good at this.
Games: Some people with slower connections cannot restock or snipe, so they rely on games. There are many fun (and some not so fun) games on the neopets site that you can earn np from. I advise you to start from here, as that is where I started out with my first 10k that I needed to get a start in the game. Although you can only send scores on your games 3 times per day, and the maximum amount of neopoints you can get per play is 1000. Although, your game score cant be higher than that, the amount of neopoints you recieve depending on the ratio the game gives you, cannot exceed 1000. People usually can make 15-30k+ doing games alone, although it is time consuming.
Hoarding: People usually buy things like medicines in bulk so when the Wheel of Excitement disease changes, they can sell their item at an inflated price. Also, avatar items such as Garlic Bread Halves, can also give you maximum profits. New avatars found in the unreleased thread may give you a hint as to what to hoard in order to get the avatar.
Reselling: It isn't buying unbuyables, but rather buying easy to sells at a low price and then selling them for the going rate. And, it isn't hard to do at all--though you need to have a good memory, play often enough to know when things are rising/lowering in price, and be able to maintain the boredom of continually refreshing on the shop wiz. It isn't for everyone, but if you are good at it, you can make a whole lot more nps than games would ever give you. -Morningstar
Questing: There are many Quest Givers around Neopia, such as the Snow Faerie, or the Esgophagor. These quests can be profitable if you have a bit of luck. No, not the ones Illusen/Jhudora give you, those are bearly profitable. Well, unless you're uber rich and some how, magically happen to have all the unbuyables they ask for.

I generally use the Snow Faerie, the Esgophagor and sometimes Edna. -watericesage
That is all the strategy I know, although, I'm too lazy to do any of those and just let my 1mil sit in the bank and sometimes buy gifts with them to send to people.
Are there any other strategies that some people prefer to making np? i'd love to hear them (and I hope they don't require too much effort.

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