Layout is key
Everything on an airship is done by airsailors, so if they can't get the coal to the engines or the ammo to the guns or the water to the fire, things will go badly. Make sure that the crew can move around efficiently. They can move much faster through corridors than through busy modules. Also, pay attention to ladders: in this ship, it looks like the coal and the suspendium chamber are really close together, but actually, the crew have to take a huge detour to fuel the chamber.
Making your ship fast
The height of your ship determines its air resistance, so make a long slim ship if you want it to go fast. But note that such a ship can't move up and down very quickly.
Making your ship tough
Modules are stronger if they are adjacent to other modules - compact ships are tougher. Keels, no matter where they are placed, increase the strength of all modules in the ship.
Uparmour the vulnerable and important parts of your ship: weapons, suspendium chambers, etc. Crew quarters have no function during combat, and keels are very tough, so they don't need armour so much.
Have enough crew to run the ship and do firefighting even when some of them are injured or dead.
Service ceiling
A heavily armed and reinforced ship is going to be very heavy and have a low service ceiling. (It can't go up very high.) Ships get a bonus to aim if they are shooting down at their target, so this matters. If you have a very low service ceiling, consider grounding your ship to free up crew for repair and firefighting.
Weapons
Rifles do limited damage, but are cheap, quite accurate and reasonably effective against lightly armoured targets.
Cannons are all-rounders: decent accuracy, fire speed, damage, etc.
Grenades: huge damage, but very very limited range, and you can't shoot upwards - you better have a higher service ceiling than your opponent or you're toast.
Gatling guns: good damage, low accuracy, great against light targets.
Rockets: lots of damage, incredibly inaccurate - either go right up to the target or at least use aimed fire. Great versus wooden armour.
Heavy cannon: punches through everything. But beware: incredibly expensive, and with such a limited fire arc that a skilled opponent can just stay out of its way.
That's all for now! This advice will probably change a bit as the game evolves, but it's a solid basis to work from.