Acids and Bases Acids donate hydrogen ions. If there is an acid present, odds are good that it protonates something with a lone pair of electrons.
Bases accept a hydrogen ion.
If there is a base in the reaction, look for a hydrogen for it to react with. Good candidates are hydrogens attached to Oxygen, Nitrogen, or sometimes even carbon - the E2 reaction, and acetylide hydrogens both react with suitably strong bases. Usually the metal is part of an ionic bond - the metal is the cation and whatever it's attached to will be the anion.