Vcc decoupling, how to do exactly?
High-capacity capacitors typically are polarized (electrolyte) caps. Those have the advantage of being cheap and small per capacity, but at the cost of having a high effective resistance for high-frequency currents.

Thus, although there's potentially a lot of stored energy available in a electrolytic cap, the moment that a device suddenly needs more current, it can't be drawn from the cap.

Thus, a smaller, but lower-ESR, and hence "faster", capacitor is usually used in conjunction with a large polarized one.

Whether or not that is necessary or not of course depends on your device's dynamic properties, on the stability of your power supply, on trace layout and robustness to voltage drops. So, there's no general rule of thumb other than "if you need as much capacity that you'd use a polarized cap, it's usually necessary to also have a ceramic bypass cap". The actual demand must be calculated, or, more realistically, just done by experience or reference schematic.