In theory, you can inject drugs into any vein. The veins most "typically" utilized by addicts and medicals professionals alike are known as Peripheral Veins, meaning that they are not located in either the stomach or the chest. The veins used for IV injection are chosen based upon ease of access, health of the vein and if you're receiving an IV catheter, an attempt to locate said catheter in an area where the patient is less likely to bother it by say, rolling over in their sleep. This is why the top of the hand is a common choice for professionals. They shouldn't be for you, as a novice.
Back to the "ease of access" comment. The reason you always see folks going for the crook of their elbow (either the Basilic or the Cephalic, not everyone's veins are identically located) is that these veins are comparatively large and easy to find and access. In general, the larger the vein, the more robust and resilient it's going to be in the face of repeated injections i.e. not the veins in your hands.
In theory, the only veins you can't inject into aren't veins at all, they're arteries. The fact that arteries carry oxygenated blood under high pressure away from the heart, causes a lot of problems when they are hit. Not only is this extremely painful, but will probably require medical attention. An artery hit will generally consist of a sharp, intense pain and blood physically shooting up your syringe, not lazily entering like it would from a vein.
Luckily, arteries in general lie lower beneath the skin than veins, so it shouldn't be by any means a common occurence. It becomes more risky when you begin utilizing areas such as the neck and hands; areas where there are dense bundling of nerves/veins/arteries.
I would highly recommend against trying to teach yourself how to IV. It can be done, but it's a lot easier to just have someone show you how to do it.
