Hi Luis. I echo the previous advise given on this topic. There can be a number of reasons why your feet are sliding. Most likely, your body structure is wrong when you are doing the exercise. Check the placement of your hands in relationship to your hips during the starting position, you want to feel your bodyweight sinking straight into the ground with no strain on your elbows. If your shoulders are stiff, or perhaps your biceps and forearms, then there is a chance that your hands are placed to far to the front causing the movement to drive your body forward when you do the lift. Also keep your feet at the proper distance in line with your hips! And remember to ALWAYS keep your spine straight, it should feel like it is elongating not compressing! Find this in the initial position and maintain during the exercise. Another possibility is that you have a muscular imbalance, once again causing you to drive your body forward instead of up. Just keep pracising at a controlled pace and as you get stronger and more flexible your execution of the movements while improve. And yes, a yoga mat or pair of shoes with good soles will help you in the meantime, just watch out so that you don't compress your body by "wedging" against the mat. That's enough of my rambling. Hope I could help in some small way. Regards CW