Take layers if travelling out of summer - temperatures can vary and can be cold at night, although we were lucky to have very warm days and mild evenings. A thin scarf is great for protecting your head and shoulders from the sun (in spring/autumn, a hat would definitely be needed in summer), or protecting your face from the wind and sand/dust if necessary. Sturdy trainers or lightweight walking shoes are recommended for Petra.
At minimum take a sleep sheet for Wadi Rum - blankets are provided if you don't have a sleeping bag but its personal preference (and if going in colder times it might be very welcome). Also take baby wipes and a torch. Sleep outside but use insect repellent, and ear plugs (even if you sleep in the tents you can't block out your fellow travellers snoring!)
If you are a diver take your diving license as there should be opportunity to dive if you wish (we got to dive from the snorkelling trip which was a bonus). Don't expect the worlds best diving though, although it was enjoyable and good value
Dont shave the day of the dead sea visit - you get this advice in your joining meeting but by then it might be too late ;o)
Be prepared for a dry(ish) holiday where alcohol is concerned. Not all restaurants will sell alcohol and if they do expect it to be expensive.
Don't be put off by the situation in the Middle East - Jordan is a safe country and they need tourists! Go now and enjoy one of the wonders of the world but without the crowds.
Some say 1 day in Petra is enough, some say you need 5 days! I think 2 is perfect, especially if you want to see the Monument and the High Sacrifice - you can take both at a leisurely pace and really soak in the atmosphere.
This trip is suitable for all ages. You don't need to be super fit but there are a lot of steps at Petra and some uneven rocks to clamber over in parts - but these are the optional sections. This would normally be an issue for me, but the rocks we climbed were very sturdy and I was pleasantly surprised at how much I could manage.
Drink lots of mint tea! It is offered wherever there is a view - a perfect combination! I also recommend the lemon and mint juice offered in restaurants, and the fresh pomegranate juice in Petra