Psychic Suits

I'm still blogging, who says I'm not? Anyway, there was a cool puzzle over at Tanya Khovanova's math blog that I've been wanting to post for a while, but I wanted to get a complete solution first. Anyway, it turns out its crazy hard, but I know enough of a solution to make it worth posting as is. Alright, here we go:

There is a deck of 36 cards, 9 cards in each of four suits. The deck is in a face-down pile in front of a psychic, who is going to guess the suits of the cards and turn them over one at a time.

The psychic makes a guess about the suit of the next card and then turns it over to see if they were correct, then proceeds to do that again on the next card. The backs of the cards are asymmetric, so it is possible to tell which way is up, and the psychic can see the back of each card before making the guess for that card. The psychic has an assistant who is allowed to orient the cards however he wants after the deck is shuffled (but he is not allowed to rearrange the cards in the deck). Before the deck is shuffled, the psychic and the assistant may communicate to plan a strategy.

What is the maximum number of cards the psychic can guarantee to get correct?

So, as an example strategy, we can get every other card easily: each two cards is two bits of information, so we simply use them to specify the suits of every other card. For example up-up means spades, up-down means hearts down-up means diamonds and down-down means clubs. With this strategy it is guaranteed that the psychic can get every other card correct, giving us 18 out of the 36 cards. Try to make a strategy that guarantees at least 19 cards. I know of a strategy that will get 24, one can also do more than that, but I don't know how, I'll give more info on that next time.