i usually focus on cruisers(if they have any) and then 2nd the capital ships with my main fleet, and a smaller fleet of light frigates to kill their light frigates. lots of focusd fire. and if i see that they are targeting one of my ships (especially a cap) i command it to run right through and past the enemy fleet so that they have to turn allll the way around to keep killing that one. I also like to split up my fleet into 2 and keep them in really loose formation so that it is harder for the enemy to employ the same tactic. I usually use fighter(as aposed to bombers) squads aswell, so that they cant make use of their bombers, and fighters still to a suprising amount of damage to normal ships aswell.
Although i havn't played many games i have been able to kill much larger fleets if they aren't using good tactics.
there is a myrid of other tactics i could explain but ill let you figure them out yourself