If the ribs have a large amount of fat on them, you can trim some of off with a knife before you even start to cook them. As for cooking to remove some of the grease, you try cooking them in a sauce pan over medium heat to try and render some of the fat away.
Broiling can work as long as it is done for a short time and with moderate heat. Remember you just want to render some of the fat off, not all of it. You also don’t want to cook the ribs, which can cook surprisingly quickly. Rendering too much fat too early in the cooking process can lead to the problems I describe below.
Try to avoid boiling in water, as this can easily go too far and dry the ribs out.
However, you will want to keep some fat in the ribs, as a lack of fat will cause them to dry out and toughen up as they cook. This is especially true in a slow cooker, where the relatively low and indirect heat often has trouble aggressively penetrating regular cuts of meat. Even something as thin and normal-sized as country-style pork ribs can dry out before they are cooked all the way through if they do not have enough fat to baste in while cooking.