If you have an even number of players, you can play in teams instead of individually. This makes the game move faster and is substantially more manageable for large groups, especially if you have fewer than the ideal number of decks on hand.
Partners sit across the table from each other so that no one discards directly to their own partner.
When playing with a partner, the table (and all scorekeeping) is shared between the two of you. Choose one player to manage the table for the team.
Since the table is shared, only one player from each team is required to formally open. Once your partner has opened, you may add freely to your shared table when your turn comes around, without worrying about point totals.
Similarly, only one player needs to be able to go out to end the hand, as always. Partners are not immune to subtracting their leftover cards, either: if your partner goes out, you must still count what remains of your hand against against your shared score.
Whereas individual players may benefit from keeping their cards a secret as long as possible, when playing with a partner, it's generally better to play what you can early on so that they know what you have and can add to it sooner.