As hinted above, for max range you want the ship to be as light as possible.
My exploration ships have the lowest number thrusters that will fit, D grade for lowest mass.
The same for sensors, life support, power distributor ( but not too low or you can't boost).
You can usually fit a much smaller shield generator -D rated - but don't expect it to last long in combat!
If you have access to the engineers, go for lightweight sensors (makes a big difference with the larger ships) .
Power unit can be a bit different. I'll go for an A rated unit (better heat management), but you may need to engineer it to have enough power. If in doubt, buy a couple of different units and store them. When you get to the appropriate engineer, transfer them to the current station and experiment.
For my deep space explorers, I fly without weapons (saving tons = more range), and a reduced size fuel tank.
If you start passenger mission look at the mass of the cabins!