A hard 5-set singles match is the greatest strain on the body and nervous system of any form of sport. Singles is a game of daring,  dash, speed of foot and stroke. It is a game of chance far  more than doubles. Since you have no partner dependent upon you,  you can afford to risk error for the possibility of speedy victory. Much of what I wrote under match play is more for singles than doubles, yet let me call your attention to certain peculiarities of singles from the standpoint of the spectator. 

A gallery enjoys personalities far more than styles. Singles brings two people into close and active relations that show the idiosyncrasies of each player far more acutely than doubles. The spectator is in the position of a man watching an insect under a microscope. He can analyse the inner workings. 
The freedom of restraint felt on a single court is in marked contrast to the need for team work in doubles. Go out for your shot in singles whenever there is a reasonable chance of getting it. Hit harder at all times in singles than in doubles, for you have more chance of scoring and can take more risk. 

Singles is a game of the imagination, doubles a science of exact angles. Doubles is four-handed tennis. Enough of this primary reader definition. 

It is just as vital to play to your partner in tennis as in bridge. Every time you make a stroke you must do it with a definite plan to avoid putting your partner in trouble. The keynote of doubles success is team work; not individual brilliancy. There is a certain type of team work dependent wholly upon individual brilliancy. Where both players are in the same class, a team is as strong as its weakest player at any given time, for here it is even team work with an equal division of the court that should be the method of play. In the case of one strong player and one weaker player, the team is as good as the strong player can make it by protecting and defending the weaker. This pair should develop its team work on the individual brilliancy of the stronger man. 

The first essential of doubles play is to PUT the ball in play. A double fault is bad in singles, but it is inexcusable in doubles. The return of service should be certain. After that it should be low and to the server coming in. Do not strive for clean aces in doubles until you have the opening. Remember that to pass two men is a difficult task. 
Always attack in doubles. The net is the only place in the court to play the doubles game, and you should always strive to attain the net position. I believe in always trying for the kill when you see a real opening. "Poach" (go for a shot which is not really on your side of the court) whenever you see a chance to score. Never poach unless you go for the kill. It is a win or nothing shot since it opens your whole court. If you are missing badly do not poach, as it is very disconcerting to your partner. 

The question of covering a doubles court should not be a serious one. With all men striving to attain the net all the time every shot should be built up with that idea. Volley and smash whenever possible, and only retreat when absolutely necessary.