Just from what I do - 1.5 oz bourbon or rye + 1/2 lemon juice + 4 or 5 oz of good ginger ale, over ice. Change that to gin as above.
One secret to this stuff is finding a hot ginger ale - if you can find Blenheim's, give that one a try. If you wind up really enjoying ginger ale cocktails, think about buying 'local hi end' ginger ales when you see them.
http://www.blenheimgingerale.com/