Deciding how you and your partner are going to position yourselves on the court is key to be successful in doubles.
Here are the 3 possible basic scenarios and the pros and cons of each:
1) Two up -- it is when both players are at the net. This is the most favorable position, as aggressiveness pays off in doubles. There are two opponents on the other side so if you and your partner get to the net before they do, you have a better chance to put the ball away. I hear a lot people say that they don't go to the net fearing the lob. My advise is improve your overheads and communicate with your partner about who covers and chases the lob. Never let the fear of getting lobbed keep you from going to the net. Nobody hits perfect lobs all the time and at the end the odds will favor you.
2) Two back -- it is when you and your partner play at the baseline. This position should be adopted only when you face a team of good servers and volleyers and when your team is receiving. You put yourselves in a better position to defend the aggressiveness coming from the other side. You will not be able be offensive as it is hard to win points hitting groundstrokes from the baseline.
3) One up one back -- it is when one of you plays from the baseline and the other plays at the net. This is the least favorable position to be in, even though it is how you start most of the points in doubles. Due to the gap that is created between the net player and the baseline player, your team becomes very vulnerable. Many points can be won by your opponents if they manage to hit on that gap behind the net player. Get out of this position as soon as possible.
Remember that points are won at the net in doubles. Have a plan to seek the net with your partner all the time and become a better team. Good luck!