find({address: { city:"SF", state:"CA" }}) - bad
find({ 'address.city': "SF", 'address.state': "CA" }) - better
Sort specifiers
find().sort({ name: 1, _id: 1 })
!== find().sort({ _id: 1, name: 1 })
Collection indexes
collection.ensureIndex({ name: 1, address: 1 })
!==
collection.ensureIndex({ address: 1, name: 1 })