Prior to a manned mission to the Moon and Mars, there are several intermediate steps that will save vast amounts of time, effort and energy.
1) We are currently planning heavy-lift unmanned rockets, capable of carrying 100 tons of cargo into orbit. We should use these to take modular spaceship units up for assembly in orbit. They can also carry fuel and provisions.
2) The first thing we build in orbit is a big engine with fuel tanks. Its purpose is to shuttle other spaceships back and forth between Earth and their destination orbit. This saves a LOT of problems, and lets the carried ships take a lot more cargo with them, instead of fuel. We did this before, in the original Lunar landing program, but it should be scaled up considerably. The shuttle would never land.
3) Second, our first mission to the Moon or Mars should be tunneling-mining robots that can dig hard-rock horizontal shafts. Such tunnels solve many problems and are far easier to make habitable, and just generally better, than shipping pre-fab habitations from Earth. These robots could work slowly and methodically for years before manned arrival, powered by a lightly shielded small nuclear reactor brought with them. And they continue to work once people are there, continuing to improve the tunnel system.
4) Though it is still on the drawing board, if they can ever build a functioning Space Elevator, the size of missions to the Moon and Mars can be increased by a factor of 10 or more. Instead of a 200 ton spaceship, we could build in orbit a 2,000 ton ship, the size of a destroyer.
Is a Space Elevator feasible? How about just a long cable and pull stuff up? As you are pulling you would have to hold your elevation that would take just as much fuel wouldn’t it?