As an addition to Girlinhat's advice above, remember another thing about rocketry.
"Less is more."
It's easy to get caught in the trap of grossly overbuilding your rockets. You can go surprisingly far with relatively small designs, provided the overall capabilities of your rocket still hold - the Delta-V parameter Girlinhat mentioned, plus another important one called TWR, or Thrust-to-Weight Ratio.
Essentially, your rocket has to have enough fuel to go where it needs to go (delta-V), and it needs to be just powerful enough that it does not waste any of that fuel to forces like air resistance and gravity.
As a primer, aim for a TWR of no higher than 2, and no lower than 1.5. That is, when you throttle up fully and fire your engines on the launchpad, the little G-meter on the right side of the navball must jump to roughly the second notch, showing acceleration of 2G. You will notice that it drops fairly quickly from there, but it will build up again when you gain some altitude.
If you keep that acceleration of around 2G until around 20000 meters off the ground, then you're doing good. Higher up it's possible to accelerate even faster, but you should watch out so as not to overstress the rocket.
From there it all depends on what your rocket is and how much fuel your upper stages have. I recommend having at least a TWR of 1 for achieving orbit from that point, though it's possible to have a powerful but short-lived secondary booster stage to shove your ship up into space, and then stabilize the orbit with a weak but efficient engine like the NERVA (LV-N).