[OperationContract]
[WebInvoke(Method = "POST", UriTemplate = "/SavePreferences", RequestFormat = WebMessageFormat.Json, ResponseFormat = WebMessageFormat.Json)]
public bool SavePreferences(EmployeeRecord info)
{
    //Do stuff
    return success;
}

var data = {
    info: {
        //Define the object properties
    }
};

$.ajax({
    type: "POST",
    url: "Service.svc/SavePreferences",
    contentType: "application/json",
    dataType: "json",
    data: JSON.stringify(data),
    processData: false,
    error: function (m) {
        alert(JSON.stringify(m, null, 2));
    },
    success: function (m) {
        alert(m.d);
    }
})