The following is an article I came across recently and I think it is an area of the game that is not focused on enough now a days. 
Most juniors are obsessed with how hard they can hit the ball and aren't interested in learning how to win a match. 

If Plan A fails, what's Plan B?  More often than not, there is no Plan B.  This applies to players of all grades.

This article was written by Nick Bollettieri, founder of Bollettieri Tennis Academy and coach to nine No.1 players over the years.

"One of the most important skills any tennis player can have is the ability to size up their opponent quickly and easily.  Often  a player will face someone they have never played before or have never seen play before.  Knowing how to read their opponent, starting at the warm up, gives a player a distinct advantage.  Whether playing for your school, college, club or as a professional, the ability to size up your opponent is a huge advantage.

Before the Match:
During the warm up, you need to concentrate on getting yourself physically and mentally prepared for the match.  But it's important to also keep an eye on your opponent as they warm up.  Here are a few things to be watching for:
> Stroke Preferences - Hit your shots down the middle and see if your opponent favours one side over the other.  For example, do they run around their backhand to hit a forehand everytime?
> Strokes - Does your opponent practise all the strokes in the warm up? Some players will skip volleys or overheads.  Others will only hit one or two balls before changing to something else.  This could give you an indication as to their strengths and weaknesses.  Hint: Players typically warm up with their strengths.
> Court Position - Hit ground strokes to them and determine where they stand on the court.  Do they come forward to the ball?  Are they aggressive?  Include a few lobs, hitting a few over their opposite hitting shoulder and seeing if they come forward after the overhead.
> Serving - Does your opponent only practise their first serve, blasting it all around the court?  How many serves do they hit?  Are they in control of their swing and can they control the ball?  Does the ball seem to go in the same direction all the time, or do they rotate the placement of their serve?

Studying your opponent in these four areas will give you an excellent read of their game before the match begins.  Any advantage you can gain from the warm up will be a huge boost for you throughout the match.

During the Match:
Now during the match, there are some things you can do early that will determine your strategy on how to win.  Many of today's players will stay on or near the baseline.  They will usually have one big weapon they use to dictate play and only come to the net behind an attacking shot for the easy volley to finish a point.  Here are four tactics that you can use to combat that style of play.
> High, Deep and Heavy - Keep the ball deep with plenty of topspin.  This will keep the ball out of their strike zone and force them to create their own power.
> Play Every Ball - The more balls you retrieve, the more you will frustrate this style of player.  Show them that they will have to hit it harder and harder to get it past you and, hopefully, this will force them to make errors.
> Stay Contained -  Stay within your game.  Avoid matching their power and hitting shots that are beyond you.  Accept the winners and use your mental game to force them to hit more and more from difficult situations.  Use your time between points to regain control of your intensity of play.
> Serve At Them - Take away their ability to attack from the first ball by serving at the body.

These are easy things that you can do to be a successful player.
To be a true champion on the court, you must think and play every point as if it is the first of the match - that will ensure you don't obsess about a lost point or get too confident on a single great play".

There will be times when your opponent is just too good for you and it is easier to accept this if you have a least tried something else during the course of the match. 
Always have a Plan B! you never know what might happen.