As previously mentioned, the player should empty their hand as quickly as possible in order to get Red & Blue. If the player starts with a low-level and low-cost card of any kind, they should activate it as soon as they can regardless of what it is.
Draw panels can be a mixed blessing for Mei. If the player has a high-level card in their hand that they can't play, drawing until they have to discard it might be quicker than trying to reach the norma & stars needed to play it. This will, of course, fill the hand with other cards which may potentially be worse.
Cards the player can "burn" quickly are advisable. This includes cards such as Flip Out, Saki's Cookie, and Bad Pudding, among others the latter which can be used to help the player drop a high-level card.
Flamethrower can be good since it will discard all of Mei's cards, and it can't be used to deny her from leveling up if its placed on her home. However since it required being at norma 3 or higher to use it, its generally preferred to bring other cards that are a lower level so that Mei can gain Red & Blue faster.
Bringing President's Privilege is not worth it given the cheapness of both versions of Mei's hyper. Bringing the card will only really benefit opponents.
Gift Cards are especially good for Mei, as every gift that can be added into the deck can be played on turn 1. Price of Power is the best, since it can help the player use higher-level cards out of their hand. Windy Enchantment and Lost Child are useful if the player is looking to KO their opponent. Unlucky Charm is the least useful gift to add to her deck.
If Mei is not currently holding Red & Blue, the player should be aggressive as possible, as Mei's neutral stats and flimsy health will do little to protect her.
Gift Exchange is very effective against Mei, as it will most likely give Red & Blue to someone else, who is likely to have better stats to abuse Red & Blue harder than Mei can.
While Scrambled Eve will give Mei Red & Blue, if it is used while she is holding Red & Blue, it will be put back in the deck and the card draw 3 chapters later will make it more likely that someone else will get Red & Blue.
Present Thief is similar to Scrambled Eve since it will allow Mei to gain Red & Blue after landing on it, but if she lands on it while holding Red & Blue, its more likely that someone else will gain Red & Blue since everyone will know that the trap will give them Red & Blue.
Scary Solicitation can be highly useful against Mei, especially after she's been KO'd & lost Red & Blue.