How can I praise God and send blessings and salutations upon His Messenger before saying "Ameen" to a supplication?

Your mother's advice to begin supplication with praise, glorification, and blessings upon the Prophet is good, consistent with Islamic law, and aids in the answering of prayers. This recommendation applies to the supplicant himself, whether he supplicates alone or in a group. It is not required for someone who is merely saying "Ameen" to a supplication.