Laid-Back is more of a way of life than something most people can just up and do. Take my father for example, if there is anything to worry about, he will; if there is anything to notice that is bad (ie, the carpet isn't brand new, there is a paint chip missing from a wall, something smells that no one else can smell>>I swear that's the worse one, he can smell spoiled milk a week before it sours).
I've never actually seen him fully relax; the closest was toward the end of vacation when he would almost get his mind off of work/bills/stuff for a day or two.
On the other side of the fence I'm the complete opposite. I'm not going on vacation as a job, I'm going to enjoy myself and make memories.
If you really want to try and be laid-back for a bit do this:
1: Know the general knowledge things like...don't go to MK on Monday/Saturday, pick out the things you want to do but don't set a date/time to do it, plan and get tickets to the things you want to do but same as above.
2: When you get there do what you feel like doing when you feel like doing it. When you get back at night think about what you would like to do tomorrow and if you wake up still wanting to do that then go ahead, if not then do what ever you decide then.
3: Don't try to be laid-back because if you think about it then you're not doing it. Enjoy the moment because there is no tomorrow until it gets here.
Remember, having fun is not a job; it's what happens when you're not paying attention to life. Remember when you were a kid? Yup, that's it....I guess that's why we enjoy WDW so much.