How should I change my usual draft strategy in a Two-Headed-Giant draft?
Many strategies get better or worse in Two Headed Giant. These are the same as what changes in regular sealed.

Much better:
Alternate win conditions are typically stronger as their thresholds don't change with the number of players. Making one player run out of cards in their library will cause the team to lose. Similarly having one player win the game, say with Felidar Sovereign, will cause the team to win.
Poison used to be a very strong strategy, see the Sliver Kids wining the PT, but that is no longer true. Previously just one player had to be dealt 10 poison for the team to lose, a rules update has changed it to the team receiving 15 poison.
Each Opponent effects are much stronger as well. Gray Merchant of Asphodel is the poster child for this type of card. Already strong in regular sealed and draft, the card is very overpowered in every format with more than two players.

Much worse:
Aggressive Creatures are not nearly as important in Two Headed Giant as in other formats. The increased options for an opponent to block back them much decreases value in attempting to overrun an opponent early. As does the 30 life that needs to be dealt with, it's very hard to build two decks to deal 15 damage each before the opponents can stabilise.

How things change completely:
Colour Choice. In Two Headed Giant it is likely that a team will play all 5 colours. At the minimum you'll be playing 4 colours, splashing the 5th in one of the decks is very easy. In original Ravnica block I won a 2HG draft where we played 7 colours. This means you don't want worry about what decks you are playing too early. Just take the best cards for the first 2 or 3 packs, then start to worry about filling out good curves and making decks in the second half of the draft.