It's not cheap, so do your homework
Thailand is very inexpensive for American travelers on a whole, which is probably why the 500 baht ($15) entry fee to the Grand Palace stings so much. This is another reason we suggest you read up properly beforehand and take your time while in the complex. It is very small and concentrated - you could walk around all the whole thing in a half hour if you wanted to - so while the buildings are stunning, the real value is in understanding all the historical aspects behind them.
We showed up with almost no knowledge of the Grand Palace other than it used to be the King's residence, and it turned out to be a big mistake given the lack of information available on site (unless you want to pay for a tour guide, who may or may not enhance your experience). Definitely read up on Buddhism and royal Thai history as it related to the Grand Palace before your visit. This is a good place to start for a general overview.
It's all about the Emerald Buddha
Don't miss the Temple of the Emerald Buddha
The entire complex is an architecture junkie's dream come true, visually detailed and soaked with Buddhist design. It was where the Kings of Thailand lived from 1782 until 1925, and where government operations took place up through 1932. Today, it is mainly a tourist attraction but still contains a few offices and event venues.
Many of the buildings on the complex were used in the past for historical preservation (libraries), worship, and government activity, but one stands out from the crowd for what still sits inside: The Temple of the Emerald Buddha. Legends trace its existence back over 2,000 years, coming to Thailand via India, Cambodia, and Laos. It is regarded as a protector of the country and is very deeply honored by Buddhists. It is presented very elegantly today in the Temple on-site at the Grand Palace, and many make the journey to sit and pray beneath it. There is no photography permitted, but of course, some people have broken that rule if you want a sneak peek.
The Story of the White Elephants
All over the complex, you will see statues of elephants, typically black ones. Ironically, they represent the infamous white elephants of Thailand, which have been kept by Thai kings for centuries. They were often given as gifts to the king, and the more elephants a king had, the more powerful he was said to be. Why are the statues black if they represent white elephants? That's a question we're still trying to get answered.
Dress codes are strictly enforced
Despite the hot and sticky weather, you aren't going to get away with skimpy clothing at the Grand Palace. They take the dress code very seriously, and if you show up under-dressed, they will lend you clothes to cover up. You'll want to wear long pants and a loose-fitting T-shirt at minimum, and make sure your clothes are not torn or tight.
It goes without saying that you should behave in a reasonable way when visiting any religious or government site. As you wander the complex, you will definitely see signs that say "respect Buddha." These signs are not as much directed at your behavior at the Grand Palace as they are a campaign to the outer world about showing respect for Buddha in every day life. Apparently, Buddha's image has been used by many as a means of selling souvenirs, something the traditional Buddhists are not happy about. They believe Buddha's image should never appear as decoration on any clothes or trinkets, and you can do your part by not purchasing any of these items from the shops surrounding the complex.
As you wander, you might notice that statues of Buddha are always 1) perched up really high or 2) very tall and towering over everything around it. Buddhist's believe that Buddha's image should never be looked down upon (both literally and figuratively) or used as decor. Because of this, Buddha's statues are always placed or built in high positions.