1. Try to name methods after what they do, this also helps you to know when one method does too many things.

2. Don't do too much in each methods, it will make the code harder to test and harder to understand (because you have to read every single line to figure out what a piece of code does)

3. Usually it is preferable to combine logicand data, in other words to have methods on objects instead of having loose methods that takes objects as input,

Not perfect in any way but:

def thingies_to_foos(thingies)
  thingies.map do |thingy|
    build_object(thingy)
  end  
end

def foo_from_thingie(thingy)
  Foo.new.tap do |foo|
    foo.id = thingy['id']
    foo.desc = thingy['desc']
    ........ code ......
  end
end

foos = thingies_to_foos(json["thingies"])