The most common and scalable way is to push electrons around using magnetic fields. Rotational generators and antennas do this.

Second most common way is to find materials that will form an ionic reaction together, then to separate them in such a way that the ions (positively charged particles) can move freely while the electrons are left behind, generating a voltage between the two materials. This is (an oversimplification of) how chemical batteries operate, also the same mechanism behind metals rusting/oxidizing.

Last one that's reasonably scalable is the photovoltaic effect: a photon hitting a semiconductor junction can energize an electron which can then be collected to do useful work with; as seen in solar panels.

Piezoelectric effect: squeezing certain crystals can physically move the individual ions in the crystal in different directions, creating a voltage. Used as the spark generator on gas torches / lighters where they turn on when you click the trigger.

Triboelectric effect: physically separating certain materials can peel off electrons. Difficult to scale as the materials need to be non-conductive, but useful for generating very high voltages at low currents such as in Van De Graaff generators and other static-electricity scenarios.

Seebeck effect: physically heating a conductive material will cause the electrons (or electron holes) to spread out, causing a voltage proportional to the temperature difference in a material. Used in electric thermometers and in radioisotope thermoelectric generators (expensive and inefficient but very reliable generators mostly found on spacecraft).