I want to host a giveaway on my blog... Any advice?

I would like to host a Halloween-themed giveaway featuring 4 books.

I've never done a giveaway so I have a couple questions.

First of all, in your experience, is it best to have 1 winner (take all) or seperate winners?
Does it draw more entries when there is more than one chance to win something or when you have a chance to win a "bundle"?

Also, what's been your experience with international giveaways?

Any advice you can offer is greatly appreciated.

Thanks!

Jessica
A BookLover's Diary