Imam Nawawi (rh) mentions in his book “al Adkhar” page 333, that the day of ‘Arafah is the best day of the year for du’a. So, a person should free themselves up and increase in making du’a, doing dhikr and reading Qur’an. One should make du’a with many different types of supplication and many different types of dhikr.
One should make du’a for themselves, their parents, those close to them from their family, their teachers, their companions, their friends, those whom they love, whoever has done good for them and for all the Muslims.
They should also take extra precautions of falling short in any of these as this day isn’t something to be missed out on and it can’t be made up.