First pass, I prefer 2 or 10 just above co-alt passes, rolling in from a dive set up about 1.5 or 2K away. The dive gives more speed, lessening gunner reaction, and being just about co-alt allows me to go nose low or nose high, depending on where I think the gunner is sitting.
I dive from about 2K advantage, parallel to buff flight path, roll in at about a 60 to 70 degree angle to pull lead, and aim for wingroot or cockpit on all types except the Lanc.
Lancs, depending on what I'm in, I do this always nose low, pull up and slash through the 2 to 3 oclock from underneath. Why the brits thought a buff without a ball turret was a good idea, i don't know.
Second pass, depending on plane, I set up from the opposite side and make it look like I'm doing the same thing, but end up pulling further out ahead, and come in from low 12 oclock, through formation. A low 12 pass seems to be difficult for most gunners to accurately target, after seeing the first pass....I don't know why this is, but I hardly EVER get hit in this pass. (999000 is a glaring exception to that, but he's money in all positions in Buffs.