How do we understand if a particular group is o-p directing or m-directing? Is there any shortcut method to do so?

Type 1- All groups having a lone pair at the key atom are ortho, para-directing groups. For example, -X, -O-, -OH, -OR, -OCO-R, -NH2, -NHR, -NHCOR etc.

Type 2- All groups having their key atom multiply bonded to more powerful element are meta--directing groups. For example, -NO2, -CN, -COOH, -COR,-SO3H etc.

Type 3- Alkyl groups are ortho, para-directing groups. whereas -CX3,-(NR3)+ are meta--directing groups.

The directive influence can easily be decided by drawing the resonating structures of the intermediate after ortho, meta or para - attack and comparing their stabilities.