Hello! Welcome to the community 
My advice:
what’s the 20 percent would account for 80 percent of your work while developing with the Meteor framework?
- The combined simplicity and flexibility of the API which allows you to prototype and iterate quickly and efficiently.
What are the things I should learn first in order for me to build most of my app and then worry about the details later?
- Best practices/options for things such as routing.
- Know that Kadira is available to help with your debugging
What methods/functions do you keep using over and over that you consider a must-know from the start?
- I think this is fairly app-specific, though I recently made a simple “wrapper” function for
console.logthat will only run in debug mode - saves me from removing them later on
- & as you mentioned, underscore is used by Meteor and provides many useful functions already.
Are there any patterns which I should learn first?
- Familiarise yourself with Meteor packages and it’s API. It allows you more control over file load order, re-usability and modularity.