I want to start a new world but every time I've tried in the past my games breaks down halfway. I'd like to know what mods I should give priority to in order to have the most smooth experience. I currently haven't started picking out mods yet but I know that the order in which they are loaded is very important. If anyone can help me feel free to comment!
Without knowing what mods you are using, we can't tell you what order they should be in.
Basically, however, read the individual mods installation instructions. Some mods will specifically say, "load before x, load after y." For other you just need to use common sense (ie, if a mod has a dependency, you need to load the dependency first).