I'm kinda new, but I'll throw in my current view..
I'd stick with "Real" living things..like the live rock.. Don't add bleached dead corals, they will probably just get covered in algea and look like crap. No plastic plastic plants, but maybe you can find a few nice real ones. I don't know about Lava, but if you mean lava rock, I'd tend to stay away from that until you know precisely what it might do to affect your chemistry. A new tank may look a little bare at first, and the want to throw junk in, will be there, but I'd avoid it. Soon things will start to grow naturally, colors will show and with the addition of Live corals (under proper lighting) you probably won't ever find the need to throw non living items in just for decoration..the tank will be a decoration all its own...
Good Luck
Billb