I noticed the repetition of characters being quite frequent, and wonder if there are any rules related to this? I know that 天天 refers to "every day" and 人人"every person" but 好好 is completely different and as far as I know its meaning is something like "take care".

May be somoene has a quide in relation to this? Or is it necesary to learn each of those repetitions as if it is a separate word? (by the way, that is the way I am learning it now).