Simple Green (heavily diluted) is a great cleaner, but it will leave leather dry and more prone to cracking, so you need an additional product to add moisture back to the leather. Even pros use it. Try washing your hands with it, then see how they feel an hour or so later.
Like using a clay bar, however, you don't need to clean it unless it actually needs it. Wiping with a damp, clean paper towel will tell you. You can do more harm than good.
If you do need to clean it, you need a soft brush, a sponge, towels, a water spray bottle, etc. Then when it's dry, apply a conditioner.
Otherwise, the "all in one" cleaners and conditioners like that posted above are usually enough.