I would recommend for the beginner to take up fly tying as soon as possible. It teaches you heaps about what a fly should look like.
I have never met even a fairly good angler who doesn't roll his own. Good quality flies are expensive (upwards of 80p each) and besides, you just can't buy the flies you need. Try buying size #20 suspenders for example.
The angler who fails to tie his own flies is certainly missing out on one of the great pleasures fly fishing offers.
Tips for your flies:
Make the heads as small as possible
Keep the dressing sparse and simple.
Spiders should have only one or two turns of hackle.
When dubbing fur, dub a little at a time.
If your partner (living, not boat) is not too perturbed then keep a small fishtank and stock it with nymphs - so you can copy them (incidentally its also a great way to find out just how your flies should be fished)
Tie flies in batches - it saves time - and aim to make all flies that should look the same, actually do look the same.
If you use road-kill/shot materials then kill the bugs by deep freezing/microwaving.
Fly tying is one of those great pleasures in life. If you over-winter then it can help keep you sane.