just to ad to whats been said give them a good clean,then the most important bit is getting them soft and supple again, consider getting some bees wax to put on after you've conditioned them, bees wax will help keep them supple and repells water/moisture
Won't that make them all slippery, as its a wax? I also doubt it will do anything as once you have used the conditioner the leather wont absorb anything else. 
they will be slightly slippery after you done it but over time the leather will absorb the beeswax. beeswax is very good for leather as keeping it supple and it will out last any fancy creams you can buy from frauds etc.
