It's much easier to compete when your mind is focused on the particular point you're playing right now.
Iron grip? Tired arm?
World-class players double-fault; they do it all the time, just like us. You'd think they were way past the point of double-faulting but there are some very good reasons why it still happens, at all levels:
In singles, at all levels of play, the preferred direction for groundstroke exchanges is crosscourt, not down-the-line. Here are the reasons:
Competition does interesting things to people: It brings out their true personality, good and bad.
Your main strings are the longer ones that do most of the hard work; they're also the ones that almost always break first. Cross strings are there to support the mains.
Everybody has felt a firm handshake, a limp handshake and a "death grip."
Watch any accomplished player and you'll see a remarkably consistent set of ritualistic behavior between points.
Once I gave a lesson to a good athlete who was struggling with his serve. He loved to smack the first serve as hard as possible because when it went in, it was virtually impossible for anyone to return.
Top-level players with highly-refined strokes want consistency in their games.
Get your racket out and look at the string face. Notice particularily where there strings in the center are becoming frayed and discolored. That's your sweet spot; the exact spot where you habitually hit the ball.
Let's check your ready position:
Do you have trouble concentrating on the ball? Do you regularily mis-hit? Do you hear the sweet sound of "ponk" or something else?
Take a lesson from any tennis pro and you will notice that he or she always brings a hopper full of tennis balls to the court. Every teaching pro realizes that practicing positive changes in tennis come from repeating correct techniques over and over until they become habitual under pressure.
Tennis is a relatively inexpensive sport to play. All you really need is a strung racket, decent shoes, balls and shorts. Oh yeah, maybe a T-shirt.