The first thing not to do is to over improve. Don't make updates that are super specific to your particular taste.

Don't over-decorate. When decorating, you want to be as neutral as possible.  

Don't be present during showings. As a buyer, it's very difficult to walk around critiquing a seller's home when they are standing right there.

Don't take things personal. (I Wish!) After having done this for 20 years, there is nothing I would love more than for this to be the case but it is hard for buyers and sellers to understand that this is just a business transaction.