Men usually sit for Itikaf in Mosque and women at home. some people also sit for Itikaf for 3 days. any person who is mentally healthy, have Emaan can do Itikaf with the Intention of pleasing Allah SWT. the Intention must not be to show the world that your are very pious otherwise you will not get any Ajar for it.
As I said above its not allowed to Involve yourself in worldly activities like business, going to your wife etc.
those people who are not performing Itikaf should also try to do maximum worship and Zikr in final 10 days of the holy month because during these 10 days comes the blessed night of Laylat al-Qadr.