Sorting my Project Life Cards

Today I finialy decided that I would sort my PL cards. I have been umming an rring since I got my first Core Kit. The question I have been asking myself this morning is how am I going to sort them. I am going to store them in the plastic tray thingy that comes with the core kits. But just not sure how I am going to sort them. By colour, by jornal, by filler, by title?? I just don't know. 

Have a great day everyone.