There's a big music festival/concert called Isle of MTV (part of Malta Music Week) that takes place every July, which you might want to seek out or avoid.
There's live music everywhere at night. Keep an eye out for The Eggheads in particular. (Google "the eggheads malta")
Don't go in July or August. It's unbearably hot.
If you can find a place to stay in Valletta itself (not in Kalkara or Gżira), go for it. Only Valletta has the beautiful architecture you see in the photos.
