Getting to the Forbidden City is fairly straight forward if you use the public transit system. Tian'anmen square is right as you exit at either the east or west stop on Line 1 of the Beijing subway system. One thing you have to keep in mind is that China is big, population wise. Many people come to visit not only Tian'anmen, but also the Forbidden City and surrounding areas. Most of them are not tourists from other countries.
People are not very used to westerners in many cases, I was approached no less than 4 times, and I've heard many stories of getting swarmed by those wanted to take photos. In my case there were no requests for photos, but lots of people trying to practice their English with me. I even sat down for tea with an English teacher, and it was facinating to get to talk to a local person, even if it was a little odd and uncomfortable for an introvert like myself at times.
Tian'anmen square and the Forbidden City are connected through an underground tunnel. Getting into either area requires passing through security. This is where I warn you that almost every place you go requires passing through security in China. Even getting into the subway requires an x-ray scan of your belongings, and a quick trip through a metal detector. My last minute decision to carry a small shoulder bag with me was a great choice. This made clearing security quick and painless as my stuff was in the bag and through the scanner while I had removed all metal from myself in advance of entering.
Tian'anmen and Forbidden City complex requires not only security screening, but also an ID. Beijing is a city you visit with your passport on you. I'm very used to placing my passport in a safe in the hotel as soon as I arrive and not taking it out until I'm ready to fly out. Personally, carrying around my passport is not the most safe thing I think I could do. I even like to minimize the credit cards I carry on me at any time. If I know a place fairly well, I'll break from the habit and bring my wallet with me, but the passport always stays in the safe. This was a mistake in China, while I was allowed through the security checkpoint with my drivers license, I would advise against this, and I would not do it again. Many attractions require ID and it is prudent to carry your passport in Beijing.
Entering into the side gardens of the Forbidden City actually launch you from the busy lines around Chairman Mao and those continuing into the main area of the city, into the peaceful surrounding areas. I highly suggest entering through the side gardens if you can figure out where to go, it isn't straight forward. A Chinese art student showed me the way and gave me a quick tour of their art exibit prior to entering. I was able to purchase an art piece from him for a reasonible price that was one of a kind and I knew my fiance would love.
Entering the side gardens of the city shows the amazing architecture of the period in which everything was built. Cypress gardens are the first thing you walk through and many attractions have seperate english versions of the informational signs around the area. There is even a special cypress tree which was the first one planted on the temple grounds, by the emperor at the time
Continuing on to the next area, your first introduction to the city buildings comes up and you are launched back in time. A small waterway shows up and it's very striking how many trees and plants show up not only in the city grounds, but throughout the city of Beijing.
Walking through to the next area shows a large building with a huge courtyard of stone pavers. Outlying buildings surround the courtyard and make a beautiful scene. Due to the low foot traffic in this section of the grounds, it is almost peaceful and a perfect opportunity for wedding photos. During my walkthrough, I saw at least 5 different wedding photographers with brides and grooms taking their photos.
On to the next area bring you out at the top of the South East gardens. Greeted by a paved walkway, more cypress trees and a huge moat of sorts. Boarding the other side of the moat, is a huge wall guarding the main part of the city. From here you can exit the gardens and secure area before walking into the main area. I actually chose to walk along the water front and come in from the east side. Interestingly this didn't happen, I made it almost to the east entrance when I was approached by the aforementioned english teacher from Xi'an. She wanted to practice her english on me, and we ended up sitting down to some tea and making new friends. It was an unexpected encounter, but experiences are what I was in China for, so getting to know someone from the country was a fun experience... though the private karaoke session was a little much for me and I went on my way.
While I didn't finish the central part of the Forbidden City, I will return at some point and continue my tour. Sometimes travel takes you in unexpected directions, but an adventure is always worth a detour or two.