In his book, Think Like A Grandmaster, Alexander Kotov posed a similar question to Mikhail Botvinnik.
Botvinnik's reply was very insightful.
"Basically I do divide my thinking into two parts. When my opponent's clock is going, I discuss general considerations in an internal dialogue with myself. When my own clock is going, I analyse concrete variations."
What Botvinnik means is that a chess player must learn to analyse not just on their own time but also to keenly and conscientiously analyse as it if was their turn to move.
But what is a concrete variation and what is a general consideration?
Analysing on general considerations means that when you analyse a certain chess position, you think of a myriad of ways in which both you and your opponent are likely to respond in a standard manner. This means looking at basic principles like defending an unguarded piece or square, connecting your rooks, taking control of the center, activating your pieces etc. Kotov explains that this involves breaking a position down to its elements and formulating both a short-term and long-term plan. A short term plan can be a simple one like improving your worst piece while a long-term plan may be like establishing a blockade or establishing a winning endgame scenario.
Analysing on concrete variations means that your opponent has made a move and you start your 'tree of analysis' based on the current position of the board and you analyse by calculating each possible move and possible opponent's reply in turn. The tree of analysis can spawn multiple branches, sub-branches and in each branch, due care and consideration and thought must be given to the possible response that resides in each branch. If any replies in the sub-branches appear to be bad, either the sub-branch is removed from the tree or analysed further to see if the sub-branch warrants any further investigation.
There is no doubt that this is very strenuous mental work and for the improving chess player like myself, it is very important to know not just to manage time but also know what to do on my opponent's time.
Kasparov wasn't far off when he quipped,"Chess is mental torture."