The single most important factor in being successful at 7-Card Stud, above even starting hand selection, is paying attention and, more precisely, watching the upturned cards. There is no way you can overstate the importance, in 7-Card Stud, of noting what cards are upturned and those which were upturned but have since been folded.
The reason for this should be obvious. If a card is in somebody else's hand, or has already been folded, then you can't possibly get it and neither can any other player. Somebody may well be showing two Aces in their hand but if you have an Ace as a face down card in your hand and you saw one get folded earlier then you know with absolute certainty that you don't have to worry about your opponent making three of a kind with their powerful pair.
Similarly, you might have a handsome looking 10-10 as your face down hole cards but if someone else is also showing a 10 then you know there is only one left in the deck with which you could make your three of a kind.
Of equal importance is knowing which cards are already unavailable to you when you're drawing to a flush or a straight. If you're hoping for a flush then every card of the suit you're after which appears on the board of your opponents is one less that you can be dealt to your hand. The less there are in the deck, the less chance you have of hitting your hand. Again, the same is true when you are drawing to a straight hand.
It is not easy to remember all of the cards which have been played, especially as players fold their hand, but being able to do so will give you a huge advantage over less observant opponents. It will also save you many, many chips over an extended period of time.
One excellent way of helping you to more quickly recognise how many cards of a suit have already been played is to take advantage of bet365's facility to play with a four colour deck, instead of just the traditional red and black. When the four suits are shown in red, black, green and blue you'll find that you notice the upturned cards more quickly and easily.
Because of the absolute importance of knowing which cards are no longer available to use, 7-Card Stud is not the sort of game you should be playing when you've got more than one table open. Many Hold'em players love to be playing at several tables at once but it's not a recommended practice when you're playing 7-Card Stud.
If you don't pay full attention to the cards in this game then you run a real risk of making mistakes that could cost you hands and a lot of your precious chips!