I go for tracers in 1st and 8th guns,so these are your furthest spaced guns,I then stick in armour piercing rounds in the 4th and 5th guns,so these being your closest guns to you.
In all the rest of the guns your 2nd,3rd,6th and 7th I've got the De Wilde incendiary rounds,works for me.
But experiment,experiment and experiment,also ensure your convergence is honed too,I have 136 vertical x 228 horizontal,but again you need to experiment to find out what works for you,dial in the enemy wingspan into the gunsight and go get 'em.
And finally in the words of Sailor Malan:
'Go in quickly-Punch hard-and get out!'