Couple of tips that I've discovered.
A make your approach VERY low, I like to set my altitude well before I aproach the fleet, come in skimming the waves in autopilot.
B Do not bore straight in to the CV. This is the easiest possible shot for someone manning the 5" guns. I like to come in at about 45 degrees off the bow, but aiming for the lead DD escort. Then about the time I see yellow ack firing at me, correct aim for CV & drop.
Ext view is handy for doing some moderate jinks while staying low.
C If at all possible have someone in a fighter (preferably with a pair of 1k bombs) make a pass at the same time you do. The more targets you have over the fleet the better chances that you'll survive long enough to drop.
D Unless you are able to drop at point blank range, you have to lead the ships a LOT!
Example, in PT boat, fireing torpedoe's when the yellow ack starts shooting I typiclly put the CV Tower on the edge of my screen. Basicly shooting at a 45 degree angle to the fleet.
Hope this helps, stick with it, theres nothing like the feeling of a successful torpedeo run!
PS hopefully the ju-88 will soon have twin torpedeo loadout option.