Choose a genre. Graphic novels come in all genres, from science fiction to uncannily realistic. A few awarding winning titles you may want to start with are "Watchmen" and "Maus." "Watchmen" is written by Alan Moore and illustrated by Dave Gibbons. The book is about a group of superheroes portrayed as real people with real issues in Cold War America. "Maus" is written by Art Spiegleman and deals with the struggles of a Polish Jew during the Holocaust. The different groups are graphically represented by different animals. For example, the Jews are represented by mice and the Germans as cats.
Find a novel with an artistic style that you dig. Because of their visual style, you really need to find a graphic novel that is visually appealing to you. Otherwise it will be difficult to get through the story, even if it's really good. For example, if you liked the artistic style of the movie "Sin City," you may consider the corresponding graphic novel or some of Frank Miller's other work. If that style didn't do it for you, you probably want to avoid Frank Miller.
Pick graphic novels that are well written. Pretty pictures only get you so far, so pick well-written graphic novels. Several graphic novels have won awards, such as "Maus" which won a Pulitzer Prize.
Take in the details. Graphic novels are not as descriptive with words since you have a picture in front of you. As such, it is vitally important to take in every detail of each image you can find to understand the story in its fullest.
Use your imagination. One of the knocks on graphic novels is that they squelch your imagination. This shouldn't be true. While you do not have to create the images of places and characters in your head, there is still so much more that you can imagine. Try imagining what characters' voices sound like and how they move. Picture what takes place between frames of the novel.