Definitely install the latest beta patch first since the blue bombsights have been corrected. There are a few useful threads with even more useful videos in them:
http://forum.1cpublishing.eu/showthread.php?t=28754
http://forum.1cpublishing.eu/showthread.php?t=23546
http://forum.1cpublishing.eu/showthread.php?t=24782
These should get you started but specific questions are welcome.
The lack of horizontal stabilizer in the Blenheim is annoying, especially since you can't use 6DOF to see the target clearly on the entire approach from the bombardier's seat. Low-altitude level bombing (1000-3000 feet) is OK but any higher than that reduces accuracy considerably. Divebombing in the Blenheim works well if the flak isn't too bad.
Level bombing in the HE-111 is good now.