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With the passing of Thai King Bhumibol, are there any customs/etiquette as a traveler I should be aware of?

Even with the news that the King of Thailand passed away, I had already scheduled a trip a year ago to visit Thailand in a week or so. I understand that most of the country is in mourning -- should I be aware of any customs/etiquette as a traveler when visiting Thailand?

From the news it states that officials will be in mourning for 30 days, but the entire country will be in mourning for a year, with flags at half-mast and such. Are there expectations of travelers then for the next year that I should be aware of should I revisit Thailand again?

One must understand that Thai citizens are very sensitive about the loss of the King. Unlike political parties, where controversy is normal, HM King Bhumibol was sincerely beloved by everyone in the country.

As a foreigner, your goal can be stated in one phrase: don't make it worse. The reason is simple: many your actions that could be tolerated in a normal situation, may cause you trouble these days.

• Etiquette. You may expect many locations (more than usual) decorated with Thai flags and pictures of the King. Watch your gestures, don't point at these as someone may see this as disrespect (even though you may be talking about something else at this time)
  Doing something in a wrong way is worse than doing nothing. If you want to wai to a portrait of the King, make sure you know how to do it.
• Dress. I haven't seen any official recommendations (yet), but @jpatokal's answer (who was first to answer) seems to be quite good.
• Political. I would recommend refraining from any kind of political discussions in Thailand. Besides the Lèse-majesté law that prohibits offense against the dignity of a reigning sovereign, don't discuss even political parties of Thailand.
• Entertainment. There are no detailed information yet (from Thai officials), but one may expect the entertainment zones to be shutdown for a durable period. So if your travel is for entertainment purposes, please reconsider your visit.
• Temples. If the purpose of your travel is visiting temples, be aware about possible crowds, as many people will go to temples to pray for the King, especially in densely-populated areas.
• Police. Some areas can have restricted access. If you see armed police or security blocking some area/building, make sure you can enter — e.g. even if there's no police tape saying, "Do not cross". In case of any doubt, politely ask a policeman.

Personal opinion. If your planned visit to Thailand allows re-scheduling, do it.