What should be kept in mind while writing a very attractive PREFACE ?
Keep in mind who will read the preface. Many people will skip it, but many others will certainly want to read it.
People who helped you write a book definitely want to be acknowledged in the preface and they will read it. How you thank them for their contributions can be a challenge. You want to point out their significance to your final product without being boring.
People who had nothing to do with your book will also read the preface. Some want to see how you developed your theory, what methodologies you utilized, get ideas of their own for similar efforts, etc. Others are interested in the creative process and want to see how someone else did it.
Making all this fairly dry stuff "attractive" can be accomplished by using a light tone, perhaps with some humor, if appropriate to the topic. Also, you can point out some highlights of your research or highlight some turning points you encountered in the research or writing process.
For example, were there points where you just wanted to walk away from the drudgery of your research or writing. What happened to bring you back to it? How do you feel now about your decision?
Keeping the reader in mind, and providing a little insight into yourself, will encourage others to actually read it.