In doubles you will often be positioned at the net at the start of a point, and during the point the player starting at the back of the court should be looking for an opportunity to get to the net, as this is where points are more easily won. However, some players feel overwhelmed by the prospect of having to cover their half of the court with very little time to react. When at the net, don’t try to cover the whole width of the court but rather focus on shutting down the centre corridor. Giving up the alleys allows you to do this.
Crowding the centre of the court takes the safest option for your opponents out of play and forces them to go for a riskier passing shot into the alleys (or lob). If they get a couple by you, good for them. But don't panic just because you watched a couple of balls sail past you. Tennis is a game of percentages and a point is a point no matter how you win it. At the end of the day the odds are in your favour that, by consistently forcing you opponents to go for the alleys, they will pile up significantly more unforced errors than winners. See you on the court!