Orient needle so scarf or short groove is facing shuttle (right), long groove away from shuttle (left). At first I used one of the flimsy aluminum needle threaders with the pointed wire at the end to orient. After a while I was able to hold in fingers properly oriented and insert without the threader.
The needle stops on some of the older Davis' are not the greatest (curved or radius groove) so sometimes I have to lower the needle for the shuttle to pick up the top thread loop.
Jon