Pick a job before placing modules
Build your first ship around one job: mining, cargo hauling, or defense. Then make room for the reactor, cargo, and weapons that suit that job. Main Sequence on Steam describes a modular builder where you control those choices and can save designs for later.
Give important equipment room first
Sketch the functional spaces while the hull is still easy to change. A hauler needs a cargo plan before you fill its interior with extras. A mining ship needs a workable place for what you collect. A defensive ship needs room for weapons without sacrificing the power and propulsion it needs to get into position.
Leave some build space for equipment you may add after the first trip. It is easier to revise an open plan than to move several finished sections to fit one module.
Test the trip the ship was built for
Take a hauler through one pickup and delivery. Test a mining ship near a deposit and see whether its cargo holds enough for the return leg you intended. For a defense ship, check how it handles before committing it to protecting a station.
Once you like the result, save the design as a baseline. Make the next variant around a specific improvement, such as carrying a larger load. The saved version gives you a useful point of comparison.
FAQ
What should I design first?
Choose the ship's job, then reserve room for its essential equipment. Build the remaining layout around those spaces.
Can I reuse a design?
Yes. The official description confirms that ship and station designs can be saved and shared.
Is there one best hull arrangement?
Use the trip you want the ship to make as your test. A compact starter hauler and a ship built to defend a station have different priorities.