Goalkeeper Training
For many years, goalkeepers had to content themselves with either a lonesome solitary (or small group) training session on their own, or with the outfield players, followed by some shooting practice or a small match.
These days, goalkeepers have their own coaches - usually ex-keepers themselves - who provide specific drills aimed solely at perfecting the goalkeeper’s art.
But first for one thing that has never changed: the mentor.
The Mentor
Most good goalkeepers who have ever played had a mentor. Most average and even the poor ones probably did too. These guys are there for you through thick and thin. They’ve been there themselves: you trust them; you respect them.
For David Seaman, at Arsenal, it was Bob Wilson who was always there with a helpful word of support and advice (but more importantly support). While goalkeeping coaches are important, it is considered equally so that there is someone who can provide mental support during periods of self-doubt.
The Drills
Goalkeepers, with the introduction of specialist coaches, and the investment of time and money into the science behind the art, have therefore got many more drills and techniques they can use to improve their game than ever before. Simply watching this video of Hannover’s goalkeepers in training demonstrates a few of the myriad drills:

The Museum of Goalkeeping - created by keepers & goalkeeping enthusiasts to celebrate the Art of Goalkeeping throughout the history of football!