What is meant by a 'live' and 'dead' hand in Seven-Card Stud?

Your hand is said to be 'live' when none of the cards that would improve your hand appear among the opponent's up cards. In that case there is a very good chance that you will be dealt favourable cards over the course of the rest of the hand. Conversely, a 'dead' hand is one in which most of the cards you need have already been dealt to your opponents.

What are the most important strategy differences between Seven-Card Stud and Hold'em?

In Seven-Card Stud every player has their own board. It is important to be able to read your opponent's board and adjust your play accordingly. Furthermore, you need to be able to identify whether the up cards in play help or hinder the chances of your own hand improving, in other words, whether your hand is live or dead. It is often useful to be able to remember which up cards have been folded by players who have dropped out of the hand.

What is the best starting hand in Seven-Card Stud?

In Seven-Card Stud 'rolled up trips' is the best starting hand, that is to say, three of a kind. Any rolled-up trips is a great start, but three Aces is the most powerful.