How to choose Decoupling capacitor?
Without any particulars, a 1 &micro;F ceramic capacitor placed physically close between the power and ground pins of the device you are trying to decouple is a good generic answer.

Back in the pleistoscene, 100 nF capacitors were commonly used.  100 nF would work for most decoupling situations too, but the choice of capacitance was dictated more by what was possible to make cheaply.  Today with multi-layer surface mount ceramic caps being cheap and plentiful, there is little harm in increasing the capacitance a bit.  With proper layout, these will have less series inductance than the 100 nF thru hole caps of ancient legend.

Take a look at the impedance curves of a family of modern capacitors.  You will see there is little penalty in using higher capacitance.  1 &micro;F is enough to to the job, and are jellybean commondity items at normal logic voltages.

In one case I used a specific model of 100 pF cap for decoupling because it was a RF application, and that cap had a lower impedance at the RF frequency than any other I could find.