Similar to the Boros Heroic and Mono White Humans matchup, we want to play the control role, though the execution is slightly different. As mentioned above, against both the white-based creature decks, you generally want to kill their creatures on-sight.
However, against Mono Blue Spirits, you instead want to sit back and wait for them to act first before you respond.
Since most of their creatures are 1/1s or 2/2s, they’re not threatening unless they’re combined with Curious Obsession and/or Supreme Phantom. You do not want to kill their creatures on-sight as they’ll still then have these key cards in hand that they can deploy later.
On the other hand, they’ll try to play these cards in a spot where they have protection for it as well in the form of Rattlechains or a counterspell, so the key is to ignore their small, irrelevant creatures and then engage in a counter-war over their key cards as likely you will need two, or even three, removal spells to get through their protection. However, it is all worth it as if you can deal with these two cards, the rest of their deck is mostly air.
In this matchup, more so than against the two white decks, it is really important that you have pressure early on in the game, as otherwise they can just take it slow and play out their cards with multiple protection spells. I almost treat this matchup closer to Abzan Greasefang, where you want to be as aggressive as possible in the first two or three turns, then spend the rest of the game holding up removal spells. Since they do not have any removal spells, if you can start the game early with multiple one drops and/or an Eidolon of the Great Revel with removal up, it’s difficult for them to make their way into the game.