John McLeod supplied the following answer:
I will assume for the moment that we are talking about French suits (hearts, clubs, diamonds, spades).
The short answer is: “it depends what game you are playing”. The longer answer would be a list of the different ways that the suits are ranked in different games. Here are a few off the top of my head (rank from high to low in each case):
hearts, diamonds, clubs, spades: Preference, 500, Tysiacha
clubs, spades, hearts, diamonds: Skat, Doppelkopf, Sheepshead
spades, hearts, clubs, diamonds: Big Two (Choi Dai Di, Da Lao Er)
diamonds, hearts, spades, clubs: Pusoy Dos
clubs, hearts, spades, diamonds: Ninety-nine
spades, hearts, diamonds, clubs: Contract Bridge
People sometimes ask this question about ranking of suits because they want to decide which of two royal flushes is higher in poker. In that case, the correct answer (for the official casino / tournament game) is that in poker all the suits are equal, and that when such a tie occurs you split the pot. But some people do play with suits ranked as a house rule and several different rankings are used. See http://www.pagat.com/vying/pokerrank.html for a discussion of this.
In a way, a more interesting question would be to ask how many of the 24 possible different suit ranking orders occur in some card game.
The answer to the question “How are the cards within a suit ranked?” is similar. It could be K-Q-J-A-2-3-4-5-6-7 or K-Q-J-A-10-9-8-7-… or A-10-K-Q-J-9-8-7 or K-Q-J-10-9-8-7-… or even A-K-Q-J-10-9-8-… depending on the game and the suit.
The question is a bit easier for other suit systems. For example, in Chinese money cards the ranking order from high to low is definitely: tens, myriads, strings, cash.