Your leather should appear like how you got it the first time, shiny and looking great. If it doesn’t look like that, then it doesn’t hurt you put on a coat of good old Proofide cream on top and underneath. Let it settle for about 40-60 minutes to let the natural ingredients work their magic. Then polish off the excess cream. Please note you may need to do this more than once to make the leather better again. Check your saddle every now and then, at least every 2-3months.
A Brooks saddle should not be ridden long during very heavy showers or stored over longer periods in direct sunlight or heat, as this can damage the leather. Never ride the saddle when it is very wet. However, if it does get wet, as long as you let it naturally air dry it will be fine.
Most metals will rust over time, so please keep it out of the elements that can do this or wipe it dry. Likewise the hardware can rust, so please think about where you store your bike. Copper rivets can also discolour over time so you may need to polish them carefully, being careful not to get anything on the leather. Regular use should prevent the need for this.