Miracle is a new keyword that allows you to cast some instants and sorcery's for very little mana when you draw them. So as you draw an instant or sorcery with miracle, if it's the first card that you have drawn this turn, you can immediately reveal it. As you do so, you may cast it for its miracle cost. It doesn't matter whether it's an instant or sorcery; if you choose to cast it, you do so right away, even if it's at a time (such as your draw step) when you couldn't normally cast it. You're not required to reveal a miracle card, even if you could pay for it. You can always choose to just draw it as normal. You are also allowed to cast the first card you draw each turn if it has miracle, so if you find ways to draw cards during your opponent's turn, you get another chance for a game-breaking, miraculous moment.
The new soulbond mechanic lets creatures team up to fight side by side. When a creature with soulbond enters the battlefield, you may pair it with another unpaired creature you control. When another creature enters the battlefield under your control, if you control a creature with soulbond that isn't currently paired, you may pair it with the new creature.
-The two creatures become unpaired if either of them leaves the battlefield, is no longer under your control, or stops being a creature.
-Usually abilities on the creature with soulbond will refer to paired creatures. There are no special rules about paired creatures beyond that. The two creatures still attack separately, block separately, get targeted by spells separately, etc.
-A creature can only be paired with one creature at a time. (In other words, a pair of creatures is always two creatures.)
If you pair two creatures with soulbond, they'll both get both of the abilities they grant.
Flickering is a nickname for exiling something, then returning it to the battlefield. Which has actually never been done until now. When you "flicker" a permanent, it's treated as a new card that just entered the battlefield. This can do a lot of interesting things for you and be very advantageous.
Other than these 3 things, nothing is really new. There are not flip cards but Undying has returned. With the mechanics down pat I should tell you that it is not too late to preorder from your favorite site or card shop. Or you could just wait and it will be out in stores and card shops. Walmart (in store only) and Target also carries them and since the price is the same, go for whatever is closest. You can see some of what I am describing here on the Wizards site. Happy gaming!