The strategy I use depends on the type of buff I'm attacking.
B17s - High speed slashing dive attacks from 1-2 or 10-11oc, alternating back and forth until all ships are dead/on fire. I prefer to aim for the cockpit or wingroot area. Come almost straight down, this limits the guns shooting at you to the upper turrets, and possibly the waist gun on the ship on the far side of the formation. Dive in, make a shot, and start the pull out/turn to reposition for your next attack. The key to cracking 17s is patience, trying to force/salvage a bad angle will probably put you low, in the 17s 5-7oc and 500-800yds, which means a quick trip to tower.
B26s - Similar to the 17s in initial setup, though you want more lateral seperation than vertical seperation. Come in from 10/2, using a dive to help build speed for setting up the follow on attack. Leave your nose low until you're under the upper turret's field of fire. Then pull up for the shot and continue through to set up for the next attack.
Ju88s - I use the same attack setup as 17s, though I don't worry about making the angle quite as steep. Stay ahead of the 3-9 line, and remember there's a fixed, pilot controlled mg.
Lancs - Two methods for dealing with these, depending on the initial situation. If I already have a nice altitude advantage I'll use the high slashing I use on 17s. If I'm closer to the lanc's altitude I'll use low beam attacks. Start in from about 1-2oc and get under the upper turret's line of fire. The idea is for the lanc to cross your firing position with you at its 3oc. I usually go for the wingroot area when using this attack. This is also the only attack where I'll push the nose and pass the buff over my canopy after I fire. The path for setting up for the next attack is easy to track from the upper turret if you pass above the lancs.
Bostons and the Japanese buffs (ki67?) I haven't really studied these like I have the ones above. I usually just 'default' to the high slashing attack on these.
Fly the bombers, man the guns, learn thier weaknesses. Then tailor your attacks to the buffs' weaknesses.
The high slash make a good "default" attack for any buff. You could practice it to perfection and use it on any buff you come across.