They drive on the left over there, same as the UK, so take it handy on the first few roundabouts, the rental clutch will take a beating if you are not used to it. The best play is to rent a car in Malta side directly from the airport, just pick the smallest hatchback you can find because the coastal roads are narrow as anything and parking in Valletta or Mdina is an absolute game of Tetris with the walls. You can compare what is available and lock in the price here
https://getrentacar.com/en-US/malta .