Draw until you feel physically tired, then pause and work a little more
Let’s reiterate this sentence a little bit. This does not mean that you must draw as a slave until the point of total exhaustion. That’s no fun and it won’t make you happy. Instead what the sentence means is, that you should stop drawing as soon as you feel physically tired. You must rest because forcing will never work not even with drawing.
Once you get to the point when you say ‘”I’m tired I wish I could rest instead’ then go ahead and rest. Drawing is not an obligation and should never be treated as such. Also, as soon as we are obliged to do something it won’t be fun anymore. So do your best, do not draw too much instead take breaks, breath some fresh air, sleep or rest. Then, when you feel it’s time, get back to your drawing or painting with a fresh mind and continue that way.