Just put everything on wheels so you can change your mind 400 times if you want to!
OK but more helpfully.... What I did to plan my layout was make a scale drawing of my room on graph paper, marking windows and doors and outlets and light switches so I had a complete view of what was going on in the room. Then I made scaled cut-out pieces of paper for each piece of furniture that was going to go into the room or that MIGHT go into the room (getting measurements online for furniture I was considering buying), and that let me play with a ton of options without having to actually drag furniture around or invest in a bunch of stuff that might not really work out.
I KEPT all of those pieces too, and I was glad I did because after about 3 months I realized the room was not working in a couple of key ways and needed a new plan...I just busted out my envelope of pieces and re-arranged it until I was happy, and then I had a nice map for my DH to use to help me move things where they would go. Thankfully I've been happy with layout #2 for awhile now.
