As one who is still learning after 25 years, I think that you learn from as many sources as possible: books, other people, CDs, tapes, videos...
When I first became interested there were few birders around (at least where I was). So I was very much self-taught. I can remember seeing my first pied flycatcher and being pleased when I recognised it in some very rudimentary book (probably the Observer book of British Birds). I bought a field guide (for about £2)--Heinzel, Fitter and Parslow and spent quite a bit of time studying it. I was pleased when I saw my first treecreeper that I instantly knew what it was. At a very early stage I saw a hoopoe, before I'd ever heard of it, in Cornwall--though of course it was easy to work out what it was.
I remember asking the only other birder I met at Marazion Marsh where I could see a spotted flycatcher (which I'd never seen). He kindly told me to stand by a certain gate for an hour and look at every bird I saw. Sure enough a spotted flycatcher duly appeared.
The only tip I would give is to spend long enough looking at birds, not just their plumage but their jizz and behaviour. After a while you become very familiar with most of the common birds. You'll be surprised how quickly you are impressing people as you point out a sparrowhawk flying quarter of a mile away, or a flock of lapwings that are just dots in the distance.
The other thing is that when you know the common birds you have more chance of spotting something unusual. If a wader with a flock of golden plovers looks a bit paler, or stands a bit apart, it might just be an American GP, for example.
Sea-watching is a different art, in my view. I think you have to be with experienced sea-watchers to learn how to tell a grey phalarope or a sooty shearwater flying past in a gale 400 yards out to sea. But I'm sure someone will contradict me! :bounce:
Good luck.