understanding phono cartridges

so as i'm new to the analog game, i dont fully understand what makes a cartridge a good cartridge. and as such, i would like to understand better, so i can make a good decision when i buy the cart for my jvc a-l31. i dont have a whole lot of money to spend, and as it seems the tonearm on this deck is a low mass guy (i make this assumption based on the fact that its a thinner arm) i know heavier carts are out. so im looking at mm cartridges basically. any insight into what really matters in a cartridge, and suggestions that would work for me would be fantastic and greatly appreciated!