Passive learning sounds almost too good to be true.
But in fact it works, if you schedule enough time for it.
Write down important things on one (or more) pieces of paper and hang them up somewhere in your home. Preferably in a place where you often pass by or spend a lot of time.
By seeing the content over and over again (without having to actively learn it), you will know it inside and out after a while.
If you want to study for more than one subject at a time, you can use a different colored piece of paper for each subject.