You might want to check out some of the excellent and detailed tutorials about cracking WPA that we have on the forum if you are feeling uncertain about the steps. Here is a good one you can start with:
A common miscomprehension is however that the deauthorization attack will automatically generate the WPA handshake. This is not the case, the 4-way handshake will only occur when a client is connecting to the AP. If there already are some clients connected you can force them to be de-associated from the AP by broadcasting deauth-packets using mdk3 or aireplay-ng. This will effectively force them to re-connect at which point the handshake will be exchanged.
However, if there are no clients currently connected to the AP your only option is to wait for one to connect.