in addition to "The Topping Book", already mentioned, you might consider getting it's companion volume, "The Bottoming Book", by the same authors for your wife. Read them together and discuss which things seem most appealing to each of you and then use that information to find a mutually desirable starting point. As trust and rapport in the scene aspects of your relationship develop she will be able to relinquish control in steadily greater degrees. Above all don't rush things, let her find her way even as your finding yours and allow yourselves to grow together both as individuals and as a couple.