Get the cable car up to mount Faber from Sentosa island, do that for when the sun goes down.
Arab street/Haji lane area is good early evening.
Go to China town and visit the Buddha tooth relic temple. Remember to go upstairs for the actual Buddha tooth temple.
Little india.
Geylang road on an evening.
Marina bay sands hotel infinity pool if you can get up there.
Long bar at Raffles for an expensive Singapore sling (it’s not the original bar but I suppose you need to go) eat as many free peanuts as you can.
The original Singaporean tourist attraction- tiger balm gardens.
Newton circus food court.
Down to the river for loads of bars, food, nightclubs, but you could be anywhere in the world in them, same as the shopping malls.
Orchard towers is worth going to for the experience.
Good cheap food all over the place.
I stayed at the Carlton hotel last time I went, well located in the middle of things and near an mrt station.