Sollte ich alles neues aufschreiben?
I keep getting new idioms. Well, some of them are quite useful and some of them are not.
Should I take notes them, even though they aren't really useful? Or should I just do it and review them every day?
How about new verbs? Should I take notes of it also?
Ich freue mich auf Ihre Antwort.
I recommend looking up certain idioms in your native language to make sure that they aren't useful. You might want to remember some just in case you hear a native German speaker say it and so aren't lost even if you don't use them yourself. You can choose which idioms you like or which are really common to memorize, but don't stress about it because the literal translations are just weird sometimes!
Some things to keep in mind with idioms:
1) Focus on learning equivalent idioms that you find yourself using in your own language, or idioms you come in contact with frequently first. Back when I started learning idioms in Spanish I would study pretty much anything that came my way, but I discovered that some of the idioms I was studying just would not stay in my head and I realized that they were idioms that I would not typically use (therefore I would not think to use them), nor would they come up in conversation that often. Why waste all that study time on something you might use once in a blue moon? Just go over every now and then so you can recognize it if it comes up, but spend most of your time on the stuff that you use or that you see coming up often
2) Learn where the idiom comes from and see how common it is in other regions. Why waste your time learning some idiom that only pops up in Southern Germany if the vast majority of people you will be interacting with are from Berlin or Lübeck?
Verbs are similar: focus on the ones that you notice coming up often (that you don't know) first, and then branch out from there. Someday I might want to dedicate some brain power to some verb I see once in a blue moon while I am reading an article on politics, but there are other verbs that I use far more often in my daily speech and that should take study priority.
Definitely take notes! On paper or in an app (I use OneNote - it's free and on everything, and allows writing with an electronic pen if you have a device with one).
You'll be referring to the same notes often until they sink in - things like tables of pronouns, conjugations and adjective endings. Keep pages of words you commonly mix up, for quick reference. Write down any mnemonics that help you. Copy and paste any particularly helpful explanations or resources you find in the forums.
If you remember a new verb relatively easily, I wouldn't say there's any need to write it down. If you find yourself making the same mistake repeatedly, then definitely write it down (whether it's the meaning, the conjugation or the past tense forms that cause trouble). I would say that Duolingo natively lacks this emphasis of getting you to focus more heavily on your weak areas, so you can definitely improve your learning efficiency by making note of this yourself.
Taking notes will also set you up well for continuing your language-learning post Duolingo (that day will come!), where studying from textbooks requires much more self-motivation and organisation.
As for idioms... each to their own. I wanted to learn the main grammar elements first, because that will get you much farther in daily life than being able to parrot some fixed phrases you don't fully understand.