In 1921, the American Technical Society recommended correcting slippery leather by "washing it first with gasoline and then with water." No right-minded person would follow such a recommendation today, but the Society was on the right track. Slippery leather has a coating--heavy in carnauba wax or beeswax--which makes it too slick to be comfortable for the sitter. Although gasoline will certainly clear away that coating, there are safer, modern-day alternatives to achieve the same result.
Mix a solution of three parts rubbing alcohol to one part water.
Rub the solution gently over the surface of the leather, using a wet, lint-free cloth. Do not rub vigorously, or you may remove the surface color.
Allow the leather to dry completely for two to four hours.
Treat and soften the leather with a top-quality conditioner. If the leather is slippery because it is stiff, a conditioner will loosen the stiffness.
Test the furniture. It should have far more "grab" to it because you have exposed the grain and conditioned the leather.