Below is a ship role guide for the 6 hulls available in the game.

Light Hull	Role	Description
Shuttle		The Shuttle is a primarily a scout ships and early colony ship.
Corvette		The Corvette is the first Troop transport and gamble fighter/bomber. You will be hard pressed to fit a cloaking device on-board.
Frigate		The Frigate is the standard light class ship providing enough room for an acceptable arsenal. At present the only true stealth warship. Good advanced Troopship.
Heavy Hull	Role	Description
Destroyer		The Destroyer with its heavy hull, cuts light damage in half. Their advantage is relative low crew number and comparative economic production cost to Cruisers. Remember shields.
Cruiser		Cruisers have an ideal weapons hold with tolerable production and manning costs. However without effective engine research Cruisers have more moral /propaganda power than outmoding Destroyers.
Battleship		The Battleship provides massive fire-power and propaganda influence. Very spacious but need top class engines.

Basically the more advanced hull the better, but Cruisers should be the maximum till you research better engines and weapons, such as Singualrity drive. Darkmatter is acceptable destroyer and frigate engine. Antimatter engine is a good intermediate. Early engines such as gravity are best kept to light class hulls.

~ Go view Full ship specs

20K bombers is considered minimal to keep a fleet moving without taking unacceptable losses.

100-200 troops is a solid number to overwhelm ground defenses quickly.

25-100% Shield minimum based on light/heavy hull.

30 speed should be a minimum. Keep an eye on the speed of enemy fleets, having a fast fleet is good but needlessly fast has its shortfalls.

Asymmetrical Production, (best way I can discribe) is researching then building ships on near every planet in your empire. Although each planet will have poor production, because every planet is producing, you can grow a fleet quickly. This is the opposite of standard thought of a few high level shipyards. This is more commonly used in early stages to produce colonyships.

Often or not you can grab a planet in a system, grow it up to base size and produce 2-3+ colony ships. You can then thoerically send just one colonyship to a system and populate most of it, freeing up colonyships to search other systems. If others players are lazy or not using troopships, you can expand well. Best shown by adding production and travel time, often building a ship on a new colony is just that bit quicker than sending one from your HQ.

These are very useful against heavy troop defence. I wouldn’t advocate attacking planets under 28 population as you will likely kill the civilian population in the process. You must have a reasonable money/res stockpile as your empire will suffer rep and loyality penalities.

One thing to consider is the space available in a ship for certain tech. Arc's Ship Design Calc

Although Destroyers are technically twice as effective as frigates, early game Destroyers are vunerable as you will not be in a position to produce enough to form a critical mass of ships. Adding a Destroyer to a fleet can however help intimidate opposition from attacking you. Its often better to even the odds by building a mass corvette fleet bolstered by Frigates. Destroyers do come into their own once you have ok engines.

A then common mistake is not to shield Destroyers effectively. Not putting shields on your ships especially Destroyers (and above) is costly mistake as most ships will be eliminated well before they can release thier payload.

Given Cruisers cost 60-80K cogs, I would advise researching Singuality drive or at least Darkmatter first. An advantage of getting Cruisers ealier is that it reduces overall costs although will slow production. Cruisers are considered the standard Heavy ship as they often trigger end-game before Battleships enter in vast numbers.

I tend to switch to Cruisers when I am producing a Destroyer per turn and quickly running out of troops. Slower production also can help boost research if you mix science and mines.

At 120K cogs Battleships are likewise a hefty production cost increase. Opting for Battleships can bolster your fleet nicely. Tanking then exclusively producing Battleships can out strip Cruiser fleets. In Advanced games, extra doctrines such as Titan make Battleships more favourable.

Following is review by established players: “Cruisers are often the best ship, so saying destroyer is best for beginners just because of resources is needlessly defensive, shielding is also too strong as a guide for early designs.”

The above guide indicates approximately the true production cost of ships, new players can then improve thier infrastructure to match, likewise many forget to put any shields on so saying put 100% means most will put 50%.