Most complicated systems are made from subsystems. You can learn the subsystems individually and then combine them eventually, some designs may even share similar subsystems.
Even for large designs, it is good to replace, or start out with the most simplistic (to implement) solution to get the whole system running correctly, and if you would like to increase the complexity, attack one subsystem at a time.
It is good to have a basic arsenal of circuits under your belt, such as (but not limited to):
- Amplifiers (Different classes, Summing)
- Oscillators
- Filters (Active, Passive).
- Mixers (slightly more advanced).
- Power electronics (H bridge, magnetics) (not really my expertise)
It is true, that sometimes solutions have to be generated ad-hoc, but with time and practice comes the ability to intuitively create circuits.
Best thing to do is to start a project that you would be passionate about, or something that you would use most days.