There are several important tips on hanging custom art work. When you make a purchase of an original art piece you will discover that the painting is ‘ready to hang’ or it is not ready. By turning the piece and looking at the back it will become immediately apparent if the frame has been fitted with two hangers and a stout wire. Hopefully you are in luck and the painting has these already attached. When purchasing on line you can certainly ask if the painting you wish to buy is ‘ready to hang’.
If your painting arrives at your home or office without any means to hang, then you will have to either buy a ‘hanging kit’ or pay someone to make the painting ready to hang…that is a frame shop that specializes in hanging art. Hanging kits can be purchased at Hobby stores. Make sure you buy the kit that will be suitable for the weight of the painting. A store clerk should be able to guide you through this decision. Some tools will be required to do the work by yourself. Frankly, for the effort and money I would be inclined to bring the painting to a shop that does this kind of work routinely. 
Once you have the clips secured and a substantial wire cable strung between, then the next step is to locate actual studs to hang from. Finding a stud is necessary for heavier paintings – a stud or two. Studs by the way, are 16 inches on center so if possible locate and utilize two. If the painting is lighter then it is certainly possible to install anchors in drywall and then screws. Once the screws are installed in the anchors then you are ready to actually hang the painting. I recommend someone help you to guide the wire over the screws. You have to flatten the hand and reach back to insure the wire cable has ‘hooked’ over the wire. Of course make sure you have a level handy so that each screw is level to the other. Certainly give some consideration to the height of the painting off the floor – many paintings are hung too high for proper viewing. Lastly, please have adequate lighting for your new painting. Often paintings are most appreciated at night and a proper spot light which highlights the painting can be truly stunning.