Take a look at Flip by Gery Keller.
I have not read the whole book yet but it seems good so far.
I have successfully flipped 5 homes, planing ahead, knowing the local market for the home you are selecting to a extreme degree is important, knowing what home buyers really want, but better yet, are willing to pay for, helps to a great deal.
If you are investing in rentals, well once again know your market to a extreme degree before you buy anything.