Singapore is one of the few Asian countries where a westerner may feel closer to home as it is highly urbanized. If Japan is heaven for the gadget junkie, then Singapore is the promised land of IT jobs and products. The country's culture is easy to soak in. Because of the diverse population, multiple languages spoken including a mix of native and English, there are a lot of traditions and customs that you'll need to keep track of if you're staying there. If you have a short memory, then you just need to remember a few things that you should not do.
Do not Bring Chewing Gums
By now you already know that chewing gum is a no-no in the country. The details are a little blurry, however. Granted that the country had a total ban on chewing gum before, but you can bring one if it is for dental reasons. If you want to be safe, of course, just do not bring gum at all.
Do not Spit
Singapore is one of the cleanest countries in the world, and spitting is considered littering. If you are fond of spitting anywhere, prepare to cough up several dollars as you'll be fined for littering.
Do not Touch Heads
If you're in Esplanade Park just relaxing and a little kid comes up to you, do not pat him on the head regardless of how cute he is. This may be offensive to the parents and it's not because you pet the kid as you would a dog. It's because the head is considered sacred. So if you're employed in the country, it's safer to not light slap someone's cheek even if you only mean to encourage or compliment them on a job well done.
Do not Use Taxis
If you're in the country for at least a week, try to learn how to get your intended destinations via public transportation. It is a lot more effective than most countries' and is relatively cheaper than taking cabs.
Do not Go Out Without Cash
The western world is very fond of using plastic for any expenses. This will be your undoing when in Singapore. It's not that the establishments do not support credit cards. They just are not as all-around as with the western countries. Imagine really needing to use the restroom but unable to because you do not have any coins.
There are a lot of other things you should not do, but they are more about understanding Chinese and / or Malay culture. For instance, a clock is often associated with death in Chinese culture and you should not give one as a gift. Those of Malay descent will find products made out of pigs offensive. All in all, Singaporeans are friendly. You do not have to keep yourself to avoid inadvertent rudeness. Just be polite and you'll be fine.