The quality of the first 3 shots will definitely determine whether you win the point and hence the game, as captaincook states. Keep it low and flat, place it into areas that are difficult for your opponents, force them to make a weak lift to kill. Best example would be Ahsan/Setiawan.
As stated by others, the first three shots are more important in doubles than in singles (though depending on the player, if you have a bad serve/service return in singles, you're in trouble as well, but that's another topic)
Doubles is less about court coverage (in terms of being able to cover the whole court by yourself) and more about applying tactics that allow your side to be on the offense. Basically, in doubles, if you ever hit up, or place a shot badly, you open up your side for attack. If you are playing a skilled pair, they may be able to maintain an all-out offense for several shots, until they break through your defense.
Detailed breakdown of first three shots.
Options: Low serve, drive serve, flick serve.
Poor service can easily set up your opponent to put away a shot.
Service is predictable, because the low serve is expected.
Drive and flick serves are risky, as you give the opponent more of an opportunity to return the shuttle at a height above the net.
2. Return of serve:
Options: Net shot, Drive, Push, Lift, Kill (Smash, Drop, or Clear for high serves)
Inconsistency of return (net shots and kills are easy to hit into the net if you are an inconsistent player, or are under pressure).
Poor returns may set up the server.
Lifting/clearing gives away the offense.
3. Return of service return:
Options: (Net shot, Drive, Kill, Lift to return a net shot, drive, or push) (Smash, Drop, or Clear to return a lift/clear)
By the third shot, the attacking team has been established. In either of the two previous shots, either side may "lose" the offensive advantage by lifting or playing a bad shot.
If you mess up too badly in the first three shots, a skilled/aggressive team will punish you for it. Listen to commentary here (time is 8:18) for some discussion by Gillian Clark that's nicely illustrated by Ahsan/Setiawan in the background. You can also watch these videos produced by the BWF here for MD, WD, and MX.
Drill to practice:
2 doubles teams
Anyone serves (whoever picks up the shuttle).
Both teams cannot lift. Ever. 3 push-ups for a lift
The rally ends after 3 shots (the three described above)
Both teams are focusing on maintaining the offense. This means that the server will focus on performing a quality serve, and covering any short replies. The receiver will focus on giving a quality reply that places pressure on the other team.
Rinse and repeat for 5-15 minutes, depending on focus level of students. This exercise is dependent on the players being focused and aggressive, sloppy playing ruins this drill.
I am assuming if you get the service return right you should be expecting a lift or mid court shot on the 3rd. It seems a well placed push return from the service just past the net player is being used a lot now.