For purposes of ilustrate this method:  

PRINCIPAL will be the PRINCIPAL database server
MIRROR      will be the MIRROR database server
myDB         will be the database

MIRRORBackup the folder created in PRINCIPAL to store the backups

EP5022      will be the endpoint name and I will use the port 5022 to configure it

I will create an anonymous login and grant it access to connect using the endpoint, this is not very secure, so you may wan to change it

No witness is configured, if you need one, you’ll have to configure it as well

For each Database do:

Set Recovery mode, execute in PRINCIPAL:

ALTER DATABASE MyDB SET RECOVERY FULL

Create Backup Folder in PRINCIPAL(i.e. c:\backup)
Share the Backup Folder (make sure other users can modify the folder)
Create Endpoints:

         Execute in PRINCIPAL

           if Not Exists (SELECT name, role_desc, state_desc FROM sys.database_MIRRORing_endpoints where name = 'EP5022')
            Begin
             CREATE ENDPOINT EP5022

                STATE=STARTED
                AS TCP ( LISTENER_PORT = 5022  ) FOR DATABASE_MIRRORING(ROLE = PARTNER)
            End
            if not exists( select * from sys.syslogins where loginname = 'NT AUTHORITY\ANONYMOUS LOGON')
            Begin
                    Create Login [NT AUTHORITY\ANONYMOUS LOGON] from windows
            End
            GRANT CONNECT ON ENDPOINT::EP5022 TO [NT AUTHORITY\ANONYMOUS LOGON]

     Execute in MIRROR

                       if Not Exists (SELECT name, role_desc, state_desc FROM sys.database_MIRRORing_endpoints where name = 'EP5022')
            Begin
             CREATE ENDPOINT EP5022

                STATE=STARTED
                AS TCP ( LISTENER_PORT = 5022  ) FOR DATABASE_MIRRORING(ROLE = ALL)
            End
            if not exists( select * from sys.syslogins where loginname = 'NT AUTHORITY\ANONYMOUS LOGON')
            Begin
                    Create Login [NT AUTHORITY\ANONYMOUS LOGON] from windows
            End
            GRANT CONNECT ON ENDPOINT::EP5022 TO [NT AUTHORITY\ANONYMOUS LOGON]

Backup Database, Execute in PRINCIPAL 

BACKUP DATABASE MyDB TO DISK = '\\PRINCIPAL\MIRRORBackup\MyDB.bak' WITH FORMAT

Kill Connections, Execute in PRINCIPAL

                declare @sql nvarchar(1000)
                declare @spid as int
                declare processcursor cursor fast_forward for
                select  SPID
                from SYS.SYSPROCESSES p inner join sys.sysdatabases d on p.dbid= d.dbid  and d.name = 'MyDB'
                where   SPID > 50
                        AND spid <> @@spid

                open processcursor
                fetch next from processcursor into @spid

                while @@fetch_status = 0
                begin
                    set @sql = ' kill ' + convert(varchar, @spid)
                    exec (@sql)
                    fetch next from processcursor into @spid
                end

                close processcursor
                deallocate processcursor

Restore Database, Execute in MIRROR
            if not exists(select * from sys.databases where name='MyDB')

            Begin
                    Create Database MyDB
            End
            RESTORE DATABASE MyDB FROM DISK = '\\PRINCIPAL\MIRRORBackup\MyDB.bak' WITH REPLACE, NORECOVERY'

Backup Log, Execute in PRINCIPAL

BACKUP Log MyDB TO DISK = '\\PRINCIPAL\MIRRORBackup\MyDB_log.bak'

Kill Connections, Execute in MIRROR

                declare @sql nvarchar(1000)
                declare @spid as int
                declare processcursor cursor fast_forward for
                select  SPID
                from SYS.SYSPROCESSES p inner join sys.sysdatabases d on p.dbid= d.dbid  and d.name = 'MyDB'
                where   SPID > 50
                        AND spid <> @@spid

                open processcursor
                fetch next from processcursor into @spid

                while @@fetch_status = 0
                begin
                    set @sql = ' kill ' + convert(varchar, @spid)
                    exec (@sql)
                    fetch next from processcursor into @spid
                end

                close processcursor
                deallocate processcursor

Restore Log, Execute in MIRROR,

RESTORE Log MyDB FROM DISK = '\\PRINCIPAL\MIRRORBackup\MyDB_log.bak' WITH NORECOVERY'

Enable MIRRORing:

Execute in PRINCIPAL

ALTER DATABASE MyDB SET PARTNER = 'TCP://PRINCIPAL.mydomain.com:5022'

Execute in MIRROR

ALTER DATABASE MyDB SET PARTNER = 'TCP://MIRROR.mydomain.com:5022'

Now everything should be ok now, and the Database is already configured.