I've been asked a lot lately about how i attach my tail & ears. First u have to make certain ears since i dont have typical cat-like ears, that would connect to skin rather than hair.
The tail is easy; take the desired tail and at the point of attachment sew on some type of flat smooth material (i use a liquid latex piece)
http://www.spirithalloween.com/product/spirit-gum-and-remover/ use this & attach to desired spot. it holds very well once dry.