Start playing for a short time, and gradually increase.
Do not start playing too many tables, gradually increase and keep a number that is comfortable for you, there is no problem playing few.
Schedule a time when you have no other activities, eat well beforehand, and schedule so you can take breaks to eat, or leave a snack nearby, consume water or juice, avoid to drinking alcohol to prevent having your game affected.
Use a comfortable chair, avoid bad posture, adjust the height of the monitor and the brightness so as not to force your vision too much, configure the position of the tables on the screen in an organized way.
Over time you will be able to reach your goals, avoid pushing yourself too hard, or taking shortcuts, after a few consecutive days take one to rest, go out for a while, allow yourself to always have a reward when you have good results, but nothing that can compromise your health or your results.