If you used furniture polish on the couch, remove it. Use a soft cloth and buff the surface to remove the wax. Do not use rubbing alcohol or a solvent cleaner, which could damage the leather and leave a stain. Keep buffing until the build-up is gone. If you put a lot of polish on the couch, use a commercial cleaner labeled as safe for leather to remove the polish completely.
Create your own leather cleaner that will leave the surface supple and not slippery. Use one part white vinegar with two parts linseed oil or neatsfoot oil. Mix the vinegar and oil together. Apply the mixture with a soft cloth, and leave it on the couch for at least eight hours. (Do not let anyone use the couch in the meantime.) Buff off the solution with a soft cloth, and remove all the excess oil.
Certain commercial leather cleaners can be used successfully. Avoid polishes and soaps intended for leather clothing or saddles. Never use a solvent-based cleaner on your leather furniture. Use a cleaner strictly intended for use on furniture. Failing to use the right cleaner may damage the couch beyond repair. Do not apply wax products to leather because it'll create a build-up even if it feels nice to the touch after you apply it.
To maintain the supple feel of a newly cleaned couch, avoid placing leather furniture in the path of direct sunlight. This will cause fading and cracking. Use a humidifier in the room to keep the leather from drying out. This also will reduce the need for conditioning the leather regularly and will keep the upholstery feeling supple without being a slippery nightmare.