Right now I'm using Bitcoin core and I want to use Electrum. What this procedure work with this combination?
It will work with electrum 1.9.8 but not 2.0.x because this version no longer supports private key imports. Instead it allows you to sweep private keys in which case all the bitcoins are sent to an address in your electrum wallet.
Note that imported private keys (not swept but imported) are not backed up by the wallet seed so you'll need to backup the wallet file using file > save copy. This is one reason why importing is not allowed anymore in 2.0.x and future electrum versions.