There isnt a real basic ratio for fleeting, it first i always build up cargo's to raid inactives, and make sure that on my 2 main planets i got around 150 espionage probes all the time. then i just start building up battleships, cause they work well on planets with defense to get as low lost units possible, then mostly start building up battlecruisers, and occasionally bombers and destroyers. After that i began building fodder for those fieuw times they are needed.
My ratio goes something like this right now
Destroyer: Bomber: Battlecruiser:Battleship:light fighter
1:1,5:5:25:100
Still planing on building more battlecruisers, bombers and destroyers, but those will come after my first deathstar :p
Most of the times i use cargo/battleship/battlecruiser combo's for planets with defense, if the planets are really strong protected i go full force
And for the barely defended planets i use cruisers, since light fighters will probably get some loses where cruisers will not.
Simulate every battle before you actually attack, you can do that here:
simulatorRemember, simulate first if you need fodder for an attack or not. i had battles where i could have lost hundreds of light fighters, but i only lost a dozen of battleships, that gave me a much bigger profit