Do bring an appetite. Beijing is the world capital of Chinese cuisine, with a restaurant for all regions. Beijing duck is a must (try Duck de Chine or Da Dong for the best of breed), but as the political capital, Beijing houses representative offices from far-flung provinces, most of which have their own restaurant serving authentic fare. Hunt down those from Yunnan, Sichuan, Hunan, Shanxi...and the rest.
Do stay in the centre. Beijing is a sprawling city and the traffic can be grim. The hutongs, or alleyways, in the Gulou and Dongsi neighbourhoods are great for walking, with good restaurants (try Susu for top-notch Vietnamese fare) and quirky hotels in converted courtyards (of which Courtyard 7 Hotel is the best).
Don't visit in winter. Beijing can be freezing, Stalinist, polluted and filthy. It is at its best in spring (except for the odd dust storm) and autumn, when making the pilgrimage to the Great Wall will feel a delight, not a chore, as you tick it off the bucket list.
Do set aside at least half a day for a relaxed trip to a less travelled part of the Great Wall, like Huanghuacheng. Avoid the nearest popular (and always crowded) spot, Badaling, unless you like aggressive hawking by vendors. If you go to Mutianyu, take the toboggan ride down at the end. Not historically precise, but good fun.
Don't go to the (in)famous emporiums that sell counterfeit junk to tourists, like Silk Street Market. Instead head to Spin and Phoenix Design for ceramics and Wu scarves, and Brand New China for up-and-coming Chinese fashion designers.
Do visit the new National Museum of China, just east of Tiananmen Square, to see how Chinese authorities do history. It’s a bit distorted, to say the least. Then check out the Beijing Police Museum around the corner, for an arresting view of how the coppers kept the peace going back to pre-Communist times.
Don't fall for the scams. Tourists who venture near the Forbidden City and Tiananmen Square will be approached by "art students", perhaps inviting you to tea and to practise their English. This is always a scam. The art on offer is rubbish, and the tea can cost an arm and a leg. If you’re after art, head to the 798 art district, and start at the well-curated Ullens Centre for Contemporary Art.
Don't get stuck in rush-hour traffic if you can avoid it. Start early and make your moves across town at midday.
Don't turn up your nose at a customised tour. If money is no object, high-end providers like WildChina and Bespoke Beijing will offer some things you won’t otherwise see, like cricket fighting. Or a great tailor.
Do visit a park early in the morning to see how Beijing’s retirees spend their post-dawn hours, from tai chi to backwards walking to using frictionless exercise equipment.
Don't confine your trip to Beijing. You may have heard: China is a big country. Spend a few days in Beijing, then head out to see as much of the rest of it as you can. Yunnan and Sichuan (home of the pandas) are great destinations away from the bright lights of the big cities.