As far as leather conditioners go, I have a few that I like. Sometimes I will use Lexol and sometimes I will use Race Glaze. I think it depends on the mood that I am in. The Race Glaze conditioner has a nice vanilla scent and is thicker in consistency than the Lexol. The Lexol has a scent that I have not yet been able to put my finger on, and is more of a liquid consistency.
Either way, I alllow them to sit on the surface for at least 30 minutes, and then I buff off the excess. I'll usually then wait a bit before applying the 303, but it can be done right after if you want.
Allow the 303 to dry, and then buff with a soft cloth.