The link provided by Rollo shows that book as 'not available' at Waterstones, but I still recommend getting hold of a copy. Many public libraries stock it.
I used to write wills for a living but I don't think that knowing about the 'before death' part of things helped me much when I had to deal with the 'after death' side (as executor of my father's will).
I found it incredibly easy. Furthermore, I found the local Probate Office to be wonderfully helpful.
Unless the will is incredibly complicated (which very few are) I'd advise you to accept. Remember, anyway, that any executor who is named in a will can always refuse to take on the job when the testator dies.
It's probably quite unusual for a testator to actually ask a prospective executor. I never even thought to ask the two executors of my will. (They're also the two principal beneficiaries, so I'm assuming that they'll both be keen to ensure that they each get their rightful shares!). I've since mentioned it to one of them but the other knows nothing about it.
Also, if you found things were getting a bit complicated when you came to act as executor, you could always employ a solicitor to do the work for you. You could charge his fee to the estate (as part of your legitimate expenses as executor).
Chris