Below is a basic rough guideline of capacitors that can be used for various frequencies.

For coupling a 100Hz signal, a 10μF capacitor can be used.

For a 1000Hz signal, a 1μF capacitor can be used.

For a 10KHz signal, a 100nF capacitor can be used.

For a 100KHz signal, 10nF capacitor can be used.

For a 1MHz signal, a 1nF capacitor can be used.

For a 10MHz signal, a 100pF capacitor can be used.

For a 100MHz signal, a 10pF capacitor can be used.

This is a rough estimate that will be effective the majority of the time. The only variable that could affect the above values is the resistance in parallel to the capacitor.

If the resistance in parallel to the capacitor is about 10K‎Ω or less, all the values will hold true. Usually the resistance is much less than this amount.

However, if the resistance is greater, such as between 10K‎Ω and 100K‎Ω, you can divide the above capacitor by 10; meaning you can use even a smaller capacitor. It's perfectly fine if you use the capacitor above, the coupling will work just as well. But you could use even a smaller capacitor, because if the resistance in parallel is larger, that makes the AC signal choose the capacitor path that much easier than the resistor path, because the capacitor path has much less resistance compared to the resistor if the resistor is larger. So as the resistance increases, the capacitance value can decrease. But, again, using a larger capacitor value than what is needed could never hurt. Using a smaller capacitor could.