Despite tennis hockey's vintage, no coherent regimen of techniques for goaltending (a la "butterfly" or "stand-up" goaltenders in ice hockey) have been defined; one might justly assemble many of the ad hoc forms under the rubric of "self-preservation," bespeaking adherents' well-ordered sense of priorities.
Nevertheless, for the goalie conscript fixed on defending the chain link, a few guidelines could be offered.
The body, not the racquet, is the most important barrier between the ball and the goal, and proper positioning covers myriad failures of the nerve: square to the ball, standing in the center of the goal (as seen from the perspective of the shooter), maximizes the space defended by the goalie. If circumstances allow, a judicious step toward the shooter will further increase the keeper's frame, narrowing the target space available - though this maneuver risks leaving the goal undefended from another facing, if the ballhandler is able to make a pass. The magnitude of both benefit and risk increase with the proximity of the shot to the goal; perimeter shots are best played with the intent to react and save rather than cut down an angle.
The racquet should complement the body's position, but should also be held so the keeper will be comfortable moving it; it is likely to be the nimblest accessory available to intercept an accurate shot. For positioning purposes, a racquet square to the shooter blocking off one's "five-hole" (a shot between the legs) is rock-solid. However, no single approach to blocking shots has prevailed by acclimation, and the racquet presents a maneuvering difficulty from almost any posture. Some players prefer to hold it with two hands, others with one. The position which facilitates the quickest racquet movement is probably held up, with both hands, and able to spin 360 degrees on a plane protecting the goal, like a lacrosse goalie - but the circumstances of the game make this inadvisable, since low shots are much easier and more common than high ones. A racquet held to the ground, meanwhile, moves up much more slowly than one held high will move down, and the motion from one's legs to the goalie's weak side (i.e., the goalie's left, if s/he is right-handed) can be awkward - hockey goalies rely on their glove hand to cover this side, but few tennis hockey players make any systematic or fruitful attempt to use their off-hand.
While experimentation with styles is heartily to be encouraged, the racquet does belong low in most cases, for the simple reason that tennis hockey is played close to the ground and most shots originate low. A racquet positioned to cut off the bottom sectors forces shooters into a lower-percentage shot, aiming for the extreme corners or lifting a rising shot at an angle high enough to beat the keeper but low enough to get under the crossbar. As the goal is wider than it is high, horizontal coverage is generally more important than standing at one's full height, and some goalies prefer to play with a very wide stance and the racquet laid lengthwise against the ground in between their feet.
Indeed, for shots at relatively close range, the ice hockey practice of lying on one's side across the mouth to seal the lower 30 to 50% of the goal is highly recommended for just this reason. Adapted to the hardcourt by Peter Martin, it turns the shooter's advantageous position into a liability, requiring an outstanding maneuver or near-perfect shot, other times slowing a fast break enough to allow teammates to recover. Obviously, the sacrifice of maneuverability on the goalie's part limits this form to particular circumstances, but it has proven devastatingly effective for players who don't mind bruised knees, dirty jeans, and the prospect of dental work.
On the other hand, while nearly all ice hockey shots are taken from the ice, springy tennis balls are frequently shot from an elevation. A goalie is probably well-advised to mimic the height of the shooter's racquet with his or her own, prepared to block the most direct line to the goal, and react from that position - though these shots gain wallop at the expense of control, and the judicious keeper will hardly be faulted for mounting an earnestly telekinetic defense of the goal whilst reserving the catgut for protection of any especially valued appendages.
Since the goaltender is recruited from the regular players and defensive players do not hang back unless tired or unmotivated, a goalie will often face what amounts to a "power play" against. One should therefore be particularly cognizant of ways to be an effective defensive player before any possible shot. When the ball goes to a corner, or is against the fence containing the goal mouth, the keeper should step out of the goal to obstruct a pass across the middle - the ballhandler is no threat to score from his or her position. An offensive player who maneuvers too close to the goalie is vulnerable to a check from the racquet just as hockey goalies poke the puck away from would-be scorers before the latter can shoot. Nor should the tennis hockey keeper refrain from vacating the goal when the opportunity to take possession of the ball present itself, as any other defensive player can assume the unhappy responsibility if the clearing attempt fails.
Similarly, defensive players should be ready to assume the mantle of keeper in this or any number of other situations. Alert players can even complement the goaltender against a near-certain shot - stepping into goal behind their teammate to block off more area, or using a tandem defense against the shot, with one player lying on the ground and the other behind, standing up. To date, there has not been any attempt to play multiple-goalie formations as routine defensive alignments, an endeavor that might well prove, as Edward Gibbon might regard it, alike destitute of profit and amusement.