Is the state of 'being still' a state of involving effort or effortless?

It is not an effortless state of indolence. All mundane activities which are ordinarily called effort are performed with the aid of a portion of the mind and with frequent breaks. But the act of communion with the Self is (atma vyavahara) or remaining still inwardly is perfect effort, which is performed with the entire mind and without break.

Maya (delusion or ignorance) which cannot be destroyed by any other act is completely destroyed by this perfect effort, which is called 'silence' (mouna).

... Bhagawab Sri Ramana Maharshi (Spiritual Instruction, Chapter II)