I personally don't add salt before straining but I think I'm in the minority. Some people add salt, some add salt and few drops of lemon juice. I prefer purely straining the yogurt then if I'm making a dip with it, I add salt and other ingredients to make it a dip. However, I also love using the strained yogurt as a spread over bread with fruits and honey, so that's why I don't add salt before hand.