I've lived in Singapore for 20 years, and there are 7 things tourists should never do when visiting the city-state

Singapore is one of the world's most densely populated countries, with six million people living in a land area of just 278 square miles.

I first moved to Singapore more than 20 years ago from the Philippines. Over the years, I learned the do's and dont's of living in the city-state. But I have noticed that when my friends visit Singapore, many of them unknowingly commit the same few faux pas, which can earn them stares or even an earful from locals.

Here are seven things tourists should never do in Singapore.

Hawker centers, or open-air food stalls, are a big part of everyday life in Singapore. Many tourists also enjoy dining at these hawkers for their delicious and affordable food.

Locals will often reserve seats at a hawker center by putting a pack of tissues on the table, which is locally known as "choping." Items like umbrellas and water bottles are also commonly used, so make sure to take the seat only if there's nothing at all on the table.

While bargaining with street food and market sellers in countries like Thailand and the Philippines is common, it's not the case in Singapore.

Prices are fixed at most stalls, especially at hawker centers, so refrain from bargaining — you'll likely offend locals.

One of the biggest mistakes a tourist can make is snacking at a train station (locally known as the MRT) or inside a train.

Not only is consuming food and drinks looked down upon by locals, it's actually illegal to do so — you can be fined up to 500 Singapore dollars, or $355. Even drinking water will likely earn you a stern warning from an MRT steward. Durians in particular are also not allowed on trains.

While hawker centers are one of the few public places in Singapore that aren't always spotless, diners are expected to clear their own tables after eating.

What used to be a norm is now a law in the city-state, and diners who do not return their used trays, plates, and utensils will be fined SG$300 or more. The only exception to this rule are "frail seniors" and young children who are physically unable to buy and carry food to their tables, according to local news outlet CNA.

Singapore's train lines are extremely busy, especially during rush hour, so commuters are expected to stand on the left side of an escalator in order to allow those who rushing to pass by on the right.

If you're carrying many items like backpacks and luggage in a crowded train station, it might be best to take the elevator.

Singapore has very strict laws when it comes to smoking in public — in the city center, people are only allowed to smoke in designated areas. Flouting this rule will result in hefty fines.

In public parks and beaches, anti-smoking laws are even stricter — every public park in the country is smoke-free. Smoking in public parks carry the same penalties as smoking outside designated areas in the city.

Many tourists enjoy visiting local temples, especially the Hindu temples located all over the country. But there are several rules to follow in order to be respectful to the religious customs, like taking your shoes off and washing your feet.

Other guidelines include refraining from entering shrines, sitting on the floor with your feet pointing towards priests and statues, and showing physical affection to others.