This takes some practice, and you want to start gently, because sliding the wrong way can easily turn an ankle. One important tip is to keep your front foot pointed somewhat into the direction of your slide. It’s the one that’s likely to catch in the clay and suffer a turned ankle. The back foot can afford to be sideways, because it will skip over any catches in the clay instead of getting jammed into them. Here’s a good illustration of how to slide into a forehand on clay. Note how the front foot is angled across the direction of the slide, and the back foot is tilted onto its inner edge. These foot positions offer the most twist-resistance for the ankle if the player should hit some kind of bump or slow spot on the court while sliding. Also, you should use an open stance when sliding into a forehand.