All very good advice, transitive.  I don't know if you play multi-player, beastyboiz, but I've just started that and found the strategies are alot different than I would have thought.  Even fleet composition doesn't work quite the same way.  I mainly play TEC and have found having one huge fleet and a small defence fleet, like transitive said, is the best way to go, though I usually wait til later in the game to build the defence fleet.  And deffinitely keep as many caps together as you can, the abilities can work together to greatly enhance a fleet. 

I haven't been in a multi-player game long enough to get a fleet this big, but for anti AI this what I build up to.  I have 2-3 Dunov Battle Cruisers (shield restore, and for SC heavy games the magnetize ability which causes enemy SC to crash into enemy ships and sctructures), 2 Akkan BC's for the ion bolt and target and range enhancement (ion bolt is great against caps), at least 3 Kol Battleships, and 3 Marza Dreadnoughts (these have a missile barage at level six that is devastating agains light frigates and support craft).  These caps and some support frigates (flak and the robotics cruiser) a few carriers and at least a dozen heavy cruisers dominates AI, even at Unfair level.

But most deffinitely concentrate your forces.  The old adage, "Divide and Conquer", if you are divided, you will be conquered! 

i play advent so

i usually have a small colonization/cleanup fleet that has one of each cap 5 anti structure ship 5 planetkiller ships and a handfull of support ships

and a main fleet which has most of the rest of my supply in an assorted support ships and my 11 other caps

on a more strategic level (opposed to tactical level cuz this doesnt really require much stratagy) latter in the game just spamming advent deliverance engines and leaving them on autocast

they actually get stuff done as long as you have enough of them

for defence i usually just barracade my borders defensive structures... usually holds em off until i can call back one of my fleets

TEC Sova rush diffecult to follow through on but oh so sweet if it works.

Advent really benefits from battleballs, but so does TEC because it keeps all ships in range of the Hoshikos.  I find I'm least likely to use a battleball with Vasari -- I tend to just creat small specialized fleets all off doing their thing.  This changes if I use a Skirantra strategy, then I tend to cluster more so all ships can potentially benefit from AoE repair.

In the previous post, when I said small fleets all off doing their thing, I meant fleets in different parts of the map, I meant ships grouped into "fleets" in the same gravwell.  In a larger sense, if I have multiple fleets, they are all pretty self sufficent.  5 fleets is a lot though, I try not to have more than 3, because you start getting to the point where none of the fleets is powerful enough to do much.  I just play multiplayer though, where people tend to mass more.

My strategy evolved with entrenchment. Before, i was keeping one defense fleet but now, defenses have became so powerful that i can engage a medium fleet with turrets and hangars and a full fleet with a medium upgraded starbase and a few turrets.I only do it on a few chokepoints (2 generally) to avoid screwing my economy.

So i can concentrate my forces : if i don't, my ships don't have enough firepower to take down a starbase defended by a fleet (particulary Vasari) if it has its hull points upgraded (when you attack the enemy territory, he often has a starbase in his borderline, unless you attack very early)

As i play almost only advent, it works quite well as an advent fleet with some good caps and support ship can handle a twice bigger fleet. So it's no big deal if i spend some credits into defense.

By the way, advent defenses are freaking powerful. Turrets with shield and a 50% damage bonus are hard to crash even for orgov cruisers !

If you don't have entrenchment, an other strategy are hit and run attacks with two fleets that defend the two flanks of your empire. You scout and once you have discovered an unprotected system, you attack. As they are smaller than a main fleet, you retreat everytime you are taking heavy damages to a planet with a few repair bay and then, back to war . you do it two or three times in a row and the enemy would lose tipically his caps and his long range fregates. The only thing that would remain are carriers and a few fregates.

One last thing, in defense advent carriers, a cap and some iconus gardians using repulsion supported by two hangar bays rule !

An advent fanatic !

my tactic varies with every fight, if i play tec i sometimes do cobalt / hoshi, lrm / hoshi or flak / hoshi spam early on. my followup varies a lot as well, f.ex. a fast followup of kodiak's after the initial fleet is set up. of course, carriers are my friend as well but so far i've never spammed them. won't say i never will though