Attempt every problem without looking at the manual first. Even if you only get as far as writing down the known variables and the relevant Schrödinger equation or Maxwell Boltzmann distribution, you are training your brain.
Communities like Physics StackExchange or Reddit’s r/Physics often have threads discussing these specific exercises. Solid State Physics Ibach Luth Solution Manual
Calculating reciprocal lattices and Brillouin zones. Attempt every problem without looking at the manual first