Many ways of doing it. I tend to have two variables: global.linkx and global.linky and in the player object's create event have:
if !variable_global_exists("linkx") or !variable_global_exists("linky")
{global.linkx=x; global.linky=y}
else
{x=global.linkx; y=global.linky}
Then, when you switch rooms, you can say where you want to start off in the new one, for instance when you leave the house you might put:
global.linkx=80
global.linky=100
room_goto(rm_overworld)