You’ll get a lot of “Do X with Y” ideas in response to your question. I suggest, instead, you think more stategerically about ship design. Frigates, for example, can do a number of things in the right circumstances–even AA work. They need a tractor, a high-tracking weapon or two, and enough armor to shrug off at least a few volleys of naughty fighter fire, and a shield doesn’t hurt there, either. Put one of those in formation right behind a cruiser that needs AA help and that wears down fighter packs that much more quickly.
Think about how you’re going to do damage to the enemy. Note you must do two things: drop shields and penetrate armor. Each weapon has different values for this. One alone generally won’t do. The exception is massed missile fire, which will usually do both.
Then think about at what range you’ll be doing damage to the enemy, at least if things go as you wish. That can help you decide what sort of speed profile you want your ships to have. If you go with beams/ in-close knife fighter type cruisers, you’ll want some speed on your ships. The faster you close to deadly range, the faster you start doing your damage the way you want, and the shorter time you take it on the chin without being able to answer back. Note carefully weapon minimum ranges here, too.
In addition to damage-dealing and range/speed considerations, look also at secondary systems and how they might assist your philosophy of design. There are a number of defenses that are weapon-specific. Given the number of missile spammers out there, I personally use the missile jammer quite a bit. Fighter spammers? I mentioned the tractor beam/high tracking weapon combo earlier.
I personally go for a few design types. Usually I field a swiss-army knife cruiser, the backbone of the fleet, with special-purpose cruisers, frigates, and fighters as necessary to meet the perceived challenge. I particularly enjoy looking at a set-up in online challenges and guessing what will be needed. Some people prefer a larger number of specialized cruiser/frigate designs.
Whatever your philosophy of design, we’ve come to the imponderable question of fleet arrangement and orders. You can lose AND win vs. the same enemy fleet with the same ships with different orders and different set-ups. Sometimes the contrast can be striking–change one order, alter one range-band for a ship’s weapons, move ships from here to there and voila, total victory with the same ships that just suffered total defeat.
Philosophy aside, here is a practical way to learn the basic skills that pay off in GSB. Pick a scenario from the basic list. Go for something in the 40K range, maybe 60K. Design some ships with a philosophy in mind. Try “hammer them from long range with missiles,” for example. Build missile cruisers, set the engagement range to longest missile range. Build in whatever else is needed to face that particular enemy, defense-wise. Set it up. Fight. See what happens. Lose, win, whatever: go back to deployment and move ships around. Clump them. Line them up. Spread them out. Stick one by itself in one corner and put the rest up in the other corner. Do that again but don’t stick one by itself, put everyone in one corner.
Observe the results closely.
If you’re losing, change ONE thing on those ships. Different missile system. I used to despair of imitating missile spam fleets–seemed like mine just weren’t as effective. Ah. Cruiser missiles–longer range but slower firing–act differently than fast missiles, or MW missiles.
If your ships are scattering around like crazy and being defeated in detail, try different orders. Change engagement ranges. Pay closer attention to the speeds of your ships. Ships with different speeds can be set up in a way that compensates for fast/slow ships. Sometimes Formations are the answer. Sometimes Formations are the problem.
Just watching battles can teach you a lot. Watch the ebb and flow of weapons fire. See how long it takes your enemy to blow up your cruisers. How long it takes your ships to blow up enemy cruisers. It doesn’t take a rocket scientist to see that if your cruisers take 10 seconds of fire to brew up, but it takes your ships (in a generic line vs. line situation) 20 seconds to toast an enemy cruiser, something needs to change.* Balancing offense and defense is a never-ending tight-rope walk. . . (I’m used to watching most battles at 4xspeed, where 10 seconds equals 40 seconds real time.)
*Unless, of course, you have 3x as many cruisers as the other guy.
The end result of all this trial-and-error and observation should be an increased sense of how to design and employ ships against enemy fleets. One last example: take a line of cruisers, stuck up against one end of the deployment zone. The enemy fleet spreads across the entire map. After the fighting starts, the enemy ships facing you will generally face you in battle. The enemy ships coming up or down from the other end will hit the end of your line in something like “line abreast” shape, vs. your (from the other orientation) “line astern” formation. All of those ships will fire at just one of your ships. Bad. Instead, in set-up, refuse the hanging flank (the other is secured by the edge of the map) by setting up the ships at the end of your line closer to the back edge.
. . .
When the enemy ships row their way up to you, YOUR ships will be in “line abreast” formation (facing, in this example, south), which is better in any case against whatever formation those enemy ships are after crossing a lot of the map to get to you.
YMMV, but good luck. . .