There are already instructions on how to do this on Electrum's documentation page - http://docs.electrum.org/en/latest/faq.html#can-i-import-private-keys-from-other-bitcoin-clients

The procedure is rather simple:

1) On Multibit you need to follow the steps here to export your private key(s) https://multibit.org/help/v0.5/help_exportingPrivateKeys.html
2) Then on electrum I suggest you to sweep the private keys rather than export. What 'Sweep' means is that Electrum will ask you to paste all your private keys, but instead of importing them directly it'll attempt to transfer the funds from those private keys onto an address on your current electrum wallet. This is much more useful because you can now create an electrum standard wallet (with 'Standard' selected) with a seed and you can safely write this down and uninstall electrum from your PC once the sweep is done. If you just import the private keys instead, then your wallet will not have a seed.

In order to sweep create a standard wallet and go to Wallet menu -> Private Keys -> Sweep, paste all your private keys. This will basically create a transaction on the blockchain and you'll have to pay the transaction fee, but the benefit is that you can easily backup and remember only the seed.