Elon Musk explains why his rockets are faster, cheaper and lighter than what you’ve seen before:
Some of what we’ve done is really just common sense — for example, using the same propellant in the upper and lower stages means that operationally, you only need to have one set of fuel tanks. If you can imagine a situation where you have a kerosene first stage, hydrogen upper stage, and solid rocket side boosters, you’ve just tripled your cost right there.
Also, the upper stage of Falcon 9 is simply a short version of the first stage. That may seem pretty obvious, but nobody else does that. They tend to create upper stage in a totally different way than they create the first stage.
The Merlin engine — we used it on the upper stage of Falcon 9, on the main stage of Falcon 9 and on the first stage of Falcon 1. So we get economies of scale in use of the Merlin engine.
Our tanks are friction steel welded, [aluminum] skin and stringer designed as opposed to machined aluminum, [giving us] a 20 fold advantage in the cost of materials, and our stage ends up being lighter… because geometrically, we can have deeper stringers.
So, yeah, those are some examples.