NetworkLobbyManager.cs

private List<Player> m_ClientPlayerObjects = new List<Player>();
private bool m_HasSentGameSceneReady = false;
private bool ShouldSendGameSceneReady
{
	get
	{
		return
			AllPlayersReady &&  			// are all the clients created + ready?
			Player.LocalPlayer != null &&		// and we exist as a local player
			m_HasSentGameSceneReady == false;	// and we haven't already sent the message
	}
}

private bool AllPlayersReady
{
	get
	{
		return m_ClientPlayerObjects.Count == numberOfPlayers;
	}
}

// called from Player.OnStartClient
public void OnCreatedClientPlayerObject( Player clientPlayer )
{
	m_ClientPlayerObjects.Add( clientPlayer );

	if( ShouldSendGameSceneReady )
	{
		SendLocalPlayerGameSceneReady();
	}
}

// called from Player.OnStartLocalPlayer
public void OnCreatedLocalPlayerObject( Player localPlayer )
{
	if( ShouldSendGameSceneReady )
	{
		SendLocalPlayerGameSceneReady();
	}
}

private void SendLocalPlayerGameSceneReady()
{
	m_HasSentGameSceneReady = true;
	
	// send your game scene ready message to the server here
}