>>> BC our resident will writer will be along soon
It's many years since I ran a will-writing company but I think I can still remember the basics ;-)
The advice I've given here many times before (and I'm happy to repeat now) is that anyone thinking about writing their will should get hold of a copy of this book:
http://tinyurl.com/jt6busx
It's available in many public libraries but with a secondhand copy offered on Amazon for less than £3 (inc postage) it won't exactly break the bank to buy one! (Don't worry if you find an older edition. While there have been a few changes to the law on intestacy, the basic stuff about writing a will still remains valid).
Read the book carefully and then draft your will based upon the guidance you've received from it. If at that stage you're completely confident that you've got it right, sign your will in front of witnesses and sit back happy that you've got an important task completed.
If you've got any doubts at all though about how good your draft is, take it along to a solicitor. (Even if you'd intended using a solicitor all along, I'd still advise reading that book and preparing an initial draft first. Many years before I started writing wills for a living I had my own will drawn up by a solicitor but I later came to realise that he'd failed to ask me lots of important questions which the book covers really well).