wear cotton clothing . Jeans and a t-shirt .
A wooden floor and table can help , but are not essential.
I do not use an antistatic strap either . But before I pick up a component Im going to put in the case I touch the case with the same hand , which eliminates electric potential differences between your hand and the case .
I dont believe leaving the case/psu plugged in and thus earthed helps at all . The static charge is on you so if you pick up and item that then gets close to the case you have created a path to earth and that may be what destroys your component .
Insert the processor in the board , then the heatsink , then RAM
then touch the case
then use the heatsink as a handle to maneuver the board in to the case , checking the stand offs are in the right place as you go .