Example trigger that delegates to helper class.

AccountTrigger.trg

trigger AccountTrigger on Account ( before insert, before update, before delete,
                                    after insert, after update, after delete ) {

    AccountTriggerHandler handler = new AccountTriggerHandler();

    if ( Trigger.isBefore && Trigger.isInsert ) {
        handler.handleBeforeInsert( Trigger.new );
    }
    else if ( Trigger.isBefore && Trigger.isUpdate ) {
        handler.handleBeforeUpdate( Trigger.old, Trigger.oldMap, Trigger.new, Trigger.newMap );
    }
    else if ( Trigger.isBefore && Trigger.isDelete ) {
        handler.handleBeforeDelete( Trigger.old, Trigger.oldMap );
    }
    else if ( Trigger.isAfter && Trigger.isInsert ) {
        handler.handleAfterInsert( Trigger.new, Trigger.newMap );
    }
    else if ( Trigger.isAfter && Trigger.isUpdate ) {
        handler.handleAfterUpdate( Trigger.old, Trigger.oldMap, Trigger.new, Trigger.newMap );
    }
    else if ( Trigger.isAfter && Trigger.isDelete ) {
        handler.handleAfterDelete( Trigger.old, Trigger.oldMap );
    }

}

AccountTriggerHandler.cls

public with sharing class AccountTriggerHandler {

    public AccountTriggerHandler() {}

    // -------------------------------------------------------
    // INSERT
    // -------------------------------------------------------

    public void handleBeforeInsert( List<Account> newList ) {
        // no logic yet
    }

    public void handleAfterInsert( List<Account> newList, Map<ID, Account> newMap ) {
        // no logic yet
    }

    // -------------------------------------------------------
    // UPDATE
    // -------------------------------------------------------

    public void handleBeforeUpdate( List<Account> oldList, Map<ID, Account> oldMap,
                                    List<Account> newList, Map<ID, Account> newMap ) {
        // no logic yet
    }

    public void handleAfterUpdate( List<Account> oldList, Map<ID, Account> oldMap,
                                   List<Account> newList, Map<ID, Account> newMap ) {
        // no logic yet
    }

    // -------------------------------------------------------
    // DELETE
    // -------------------------------------------------------

    public void handleBeforeDelete( List<Account> oldList, Map<ID, Account> oldMap ) {
        // no logic yet
    }

    public void handleAfterDelete( List<Account> oldList, Map<ID, Account> oldMap ) {
        // no logic yet
    }
    
}