In competitive tournaments, opening against a half-long ball is a very useful skill. It allows players a much easier time setting up their attacks, both when serving and receiving. Also, a good half-long opening can put a lot of pressure on an opposing server, especially in important points, such as 9-9. Here are some tips on how to practice your forehand opening against half-long balls. (Note - a half-long ball is when, if given the chance, the second bounce on your side of the table would be at or just barely past the edge of the table.)
First of all, when trying to loop a half-long ball with the forehand, you need to make sure your stroke is shorter than with normal loops.Because half-long balls usually drop faster than long balls, if you swing your arm too far back, you will be rushed in trying to finish the stroke. So for these forehand loops, a smaller follow-through is suggested. Focus on using your wrist to generate spin and your hip (right hip for righties, left for lefties) to generate power against backspin. (This tip could be divided into two parts, wrist and hips.)
You should focus on turning your wrist at the contact point, at the top the bounce, and try to generate as much spin as you can by going forward and a little bit upward. (The upward part depends on how much spin the incoming ball has.) Once you learn how to use the wrist properly, it becomes easier to loop against a half-long ball. Then use power from the hip at the same time you turn your wrist. Make sure the hip and wrist are in line. If the wrist goes forward, the hip should go in the same direction.
Lastly, we come to one of the most common problems for players. Although you can usually open against half-long balls, they are sometimes shorter than you think. When opening with the forehand, players are sometimes close to hitting their fingers against the edge of the table. To avoid this, you should keep the tip of your paddle a bit in front of your hand. Make sure your hand and paddle are pointed in the same direction. Do not cock or drop your wrist. Contact the ball near the tip of the paddle. That way your hand is always behind and less likely to hit the table.
Overall, opening against a half-long ball is a useful and practical technique for receiving and attacking. Using it gives you a big advantage in getting the first attack - which will lead to many more wins.