I took a look at some screenshots from league of legends. It's not really what I'd consider cartoony, but it's certainly colorful. I'm not a 3D artist but I know a bit about cartooning. The 'toony nature of a character is created partly through bodily proportions. The body shape is exaggerated toward an archetype: round with large hands feet and eyes for childlike or fat characters, bodybuilder for fighters, tube/rubberband for slender athletic characters, hourglass with tiny hands and feet for sexy female characters, etc. Cartoons also are more abstract that realistic art - removing detail to make shapes more geometric (specifically preferring curves over sharp angles) will make any object look more cartoony. A book on Caricaturing is probably the best place to find instructions about how to look at a real model and choose features to exaggerate to make that model more cartoony.

As for colors, cartoons typically use cell shading, so you could look into 3D cell shading. Also for particularly bright vivid colors, that suggest to me that the textures probably have high saturation.