First, the basics. There are many official neoshops, and each sells items which range from You-Shouldn't-Buy-It-If-Your-Life-Depended-On-It, Eh-Whatever things, OOOO-Grab-It-Now, to Oh-My-God-I-Can't-Believe-My-Luck items. As you can see, you REALLY need to know what to buy, and what to ignore. We have a growing list of the 'good' items, which you SHOULD read after you finish this guide, located on the sidebar under 'Hot Ticket Items'. You're going to need to get to grips with these items, and what they're worth. These items come into the shops in a rush, called a 'restock'. These restocks happen about 5-8 times an hour, at random times, which is where the patience comes in. You can wait for 18 minutes with nothing happening, then have 3 restocks one after another, or have a restock every 8 minutes or so, like clockwork. While you're refreshing the page, waiting for a restock, think of what your dream is, what you'll spend the nps on, and the time will pass much more sweetly. You can improve your shopping opportunities by having more than one window open at a time, refreshing to different shops. Some people like having two shops open at once, some three or four or more. Practice, and find out what's best for you. Remember, patience is the key. That's how and what to buy, but how to sell?
Apart from knowing which items to buy, knowing how to price them so that they'll sell and you'll make a profit is the most crucial part of this. Get it wrong, and you'll lose out badly, but once you learn how to do it, it becomes automatic very quickly.
Now, there are literally millions of shops in Neopia. How do you get people to come to yours and buy your items? Easy. You find out what price everyone else is selling a particular item for, and then you price your item at the lowest price, or just a little under. Result? Your items sell first, before everyone else's. If there were 10 shops in real life, all stocking the same items, you wouldn't buy from the expensive shops, would you? Same thing here. And because you sell all your items quickly, you make far more neopoints than the people who price their items expensively, but don't get people buying them. How to do this? Make friends with the Shop Wizard.
The Shop Wizard is your best friend on Neopets. He might be rather dull, and have no conversation, but he'll help you get rich like no-one else (apart from us, of course!). The Wiz is basically a list of all the items for sale from people's shops, with who is selling them and for how much. When you go to the Wiz, enter the item you want to know the price for into it, and it'll give you a page listing prices. Now, remember, this is only one page of item prices. The Wiz couldn't possibly show all the items in stock in people's shops at once, there's too many. What you do next is refresh, at least 6-9 times, to get a few pages. With every new page you're shown, remember what the cheapest price for the item is (the one at the top). When you've finished refreshing, you'll know how much to price your item at. If the cheapest price you found for the item was, for example, 1490nps, then price yours from 1475 to 1490nps.
The second point to make here is, you have to price every item every time you want to sell it. DO NOT just price it the same way you did last time. Prices change a lot, and very quickly, and you could either make your item too cheap and lose nps, or too expensive, and not sell it. 'Wizzing' is absolutely necessary, every time you want to price an item.
Now, one other vital thing to learn - how to make your shop work for you. It's very tempting, when you're decorating your shop, to put in lots of dolls, puffs, blinkies, images, music, tables etc, BUT just think - everything you add to your shop means that it takes longer for the page to load. No matter how well-priced and desirable your items are, you'll have a much harder job selling them if it takes forever for the shop to load. People will get bored waiting and go somewhere else. DO put in a background and decorations if you want to; it's fun and will make your shop much more attractive, just go easy on it. Get a friend to go to your shop, and tell you how long it takes to load if you think you've overdone it.
How big should your shop be? There's a lot of discussion about this. Some people think that the bigger your shop, the better. This isn't really true. Pricing your items well and being on the top of the Wiz list is more important than having a huge shop. Generally, make your shop the size you need it to be.