There are many ways to assign numbers to the cards, so do what makes sense to you. I decided that a spade has one sharp point, a heart has two rounded edges, a club has three “leaves”, and a diamond has four points, so:
spade = 10
heart = 20
club = 30
diamond = 40
Then, add the value of the card Ace through 10 (10 is zero, so the 10 of Spades would be 10; Ace of Spades would be 11).
And, for instance, the 9 of clubs would be 39. The 9 of diamonds would be 49. The first digit always gives me my suit and the second my card value, Ace through 10.
For face cards, I switched the suits to the ones position and assigned:
Jack = 50
Queen = 60
King = 70
So, the Jack of Hearts is 52; the King of Diamonds is 74, etc.
My numbers then go 10 through 49, then 51-54, 61-64, and 71-74.
Hope that makes sense. It made the most sense to me, but another system might work better for you.
I’m just now getting my 100 loci journey together with PAO and assigning them to the card numbers. Still lots of work to do, but it’s fun!