The data sheet has all relevant info, or you can look to see what other people have done in their circuits.
It's not usually critical for these devices.
A capacitor of around 10nF-100nF should be ok, placed close to the device. For the reset circuit, the timing is in the data-sheet. For that you can use a simple RC circuit (C connected
to ground, R connected to VCC and the common connection to the reset pin), or if you prefer, there are dedicated reset ICs. The simple RC should be fine.
There are no other components needed for the ATmega. It can even work with an internally generated clock.