How do I make restaurant-quality white wine sauce?
What kind of sauce are you making ? a simple "beurre blanc" ? a gravy (with a roux) or a cream sauce ? 

Can you describe the recipe you are using (ingredients, technique) ?

What I do (for beurre blanc):

Cook down the schallots slowly in wine; add a little bit of water and white vinegar, it should not be dry.
Use cold unsalted butter cut in small chunks
Mix in the butter with a whisk until the butter is well integrated.
Pass the mix through (sp) a fine mesh to remove the schallots.
Adjust seasonings.
...