Step1
First you have to familiarize yourself with the major modern art movements. The major art moments are Art Deco, Impressionism, Fauvism, Expressionism, Art Deco , Art Nouveau, Cubism, Surrealism, Pop Art and Op Art. Knowing these movements will help you decide what you're looking for and will direct you towards which artwork to purchase. A simple internet search will give you a vast amount of information for each of the movements and photo examples.
Step2
The second step it to identify which art movements you like best. Each modern art movement has its famous or brand artists. For example, some of the big names and their movements are Dali in Surrealism, Fauvism includes Matisse, Art Nouveau has Picasso and Impressionism has Monet. Knowing which art movement most interest you will help you narrow your art buying selection.
Step3
If you're looking for art that will have a return on investment its best to stick with a well known modern artist. Many of these artists have pieces that will come up for sale at auction. An internet search will give you a good baseline of how much the works of your favorite artists are currently going for.
Step4
If you're on a limited budget its best to purchase original modern paintings from talented emerging artists. The selection is readily available and he price difference is enormous. A good source of original modern artwork is contempogallery.com.
In conclusion, do your homework. A little legwork now will pay off big in the future. When it comes to researching your potential artists, the internet is your friend. Know what you like and know your artists.