Weight is very important in Space Agency, if you have too much weight you wont be able get into orbit. Every time you add a stage your weight increases. There are many ways to conserve fuel so that weight does not matter unless it's under 57, which I will and you can mention in the next paragraph.
Tricks to conserving Edit
- turn off the first stage when it reaches maximum velocity and the boosters you are using will keep going (unless you are using delta IV boosters)
- Quickly keep tapping the engines during ascent to preserve velocity and save fuel (but it's kinda cheating though...)
- in space you can use gravity assists when passing by a planet or star at faster than orbital speed. It points the spacecraft in a different direction without you using any fuel for turning.
- in space don't speed up too much because you could end up using double the fuel you needed to.