How to set the correct indents?

Question

Design

There is a block with text
Size of the main text and heading 14
Leading 21
Can you please tell me if there are any rules or recommendations to calculate the optimal value for the indents both between the heading and the main text, and in general for the entire text from the edges of the block?

Answer 1

vertical rhythm.
Link one
Link two
Link three
Calculator in my bookmarks

Answer 2

The rule of internal and external - look in Google.
artgorbunov.ru/bb/soviet/20140224
artgorbunov.ru/bb/soviet/20140310