How to implement/improve/ make faster this query with joins

Please bear with me I am not skilled in SQL:

I have three tables

1) Notifications - stores all my data

2) GroupTable - Has the names of groups and related id

3) GroupUser - this table maps Uname and Udob to a group from GroupTable.

Now before I fetch records from Notifications I want to check the GroupTable for GroupID take this GroupID and look in GroupUser for all the records in this GroupID (Names,DOB as these are unique) Once I get this data I want to fetch records from Notifications table for the Names and DOB's in ascending order of the date:

So far I have the following query, it works fine just that I am not satisfied and I think this can be improved:

 SELECT 
    * 
 FROM 
   (SELECT 
        * 
    FROM Notifications 
    WHERE 
          DateToNotify < '2016-03-24' AND 
          NotificationDateFor IN 
                (SELECT gu.Name 
                 FROM GroupUser AS gu 
                 INNER JOIN GroupTable AS gt ON 
                               gu.GroupID = gt._id  AND
                               gt.GroupName = "Groupn"
                ) AND
          DOB IN 
                (SELECT gu.DOB 
                 FROM GroupUser AS gu 
                 INNER JOIN GroupTable AS gt ON 
                               gu.GroupID = gt._id AND 
                               gt.GroupName = "Groupn"
                )
     ) as T 

 ORDER BY 
      SUBSTR(DATE('NOW'), 0) > SUBSTR(DateToNotify, 0)
    , SUBSTR(DateToNotify, 0)