Start a timer and sit observing your thoughts but not being carried away with your thoughts. At times you will be so carried away that you do not realise that you are supposed to be meditating, when that happens, bring yourself back to realising that you are meditating. You will slowly feel a flow state where you feel a bit positive and focused, when that happens try to be in that zone as long as you can.
Mindfulness is being aware of what is happening while it is happening without any judgement or preference.
See the energy of the thoughts and cultivate a mood of happiness and truly relax your brain intentionally. You often try to find a reason to meditate, to be better at this or that, but giving it a measurement is unfortunately counterproductive.
The default mode is what your brain does when it has nothing to focus on. It is unintentional and also unguided. It is described as follows.
If all tasks are complete: begin think of better ways to solve the past problems we had
Like all things in the mordern era, many of our old biological programming is now an evolutionary_trap. If you ever find yourself compulsively ruminating over the past (as I do many times) then consider methods to stop doing, as it is proven to cause anxiety (and therefore depression) and is not good for focus.
Arguing with someone in your head, or talking to yourself is not something you would do if you were aware of it. It is often regarded as “the first sign of madness”