This flow chart is general and assumes the substrate is aromatic.
Are the reagents strongly electrophilic or stongly nucleophilic? Generally Electrophilic reagents have some sort of strong acid involved (AlCl3, NHO3, etc.). Strongly Nucleophiles involve some sort of strong base (NH2, OH)
Does the substrate have a good leaving group? (e.g. Br, Cl?)
Does the substrate have one or more electrons withdrawing group ortho and or para to the leaving group?