Learn almost everything.
Basic electronics: Network theorems, RC-RL Circuits, 2 port networks, dependent sources, frequency domain characteristics
Control systems: time domain, frequency domain, transfer function, bode plots, Nyquist theorem, stability issues
Analog electronics: Diode clipper and clamper circuits, BJT biasing and small signal analysis, FET biasing and small signal analysis, multistage amplifiers, differential amplifiers, CMOS analog circuits and layour, OPAMP stages, feedback concepts, oscillators, active and passive filters and the list goes on. Nowadays most ICs are CMOS based, so that's a really good topic to focus on.
Signals and Systems: Basically everything starting from Fourier Series, Fourier Transform, DTFT, CTFT and DFT to LTI systems and system analysis. Most dealing in analog design are based on continuous time so more foucs should be laid on concepts dealing with the same.
Power electronics: DC-DC converters, Buck, Boost and Buck-Boost regulators, inverters, rectifiers, PWM techniques (mostly these but there may be other topics as well based on your profile)
Basic concepts of communications such as modulation techniques, bandwidth concepts, desing of transmitter and receiver for analog communications and noise.
Have all these at your fingertips, which isn't really easy. Then you're good.
Catch up with newer tech like Multi-gate devices and spintronics. Learn on the go.

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