Do dress for the weather
This is an absolute no-brainer. Remember to pack all your summer outfits suitable for Singapore's tropical climate and warm temperatures that range from 24 (rarely) to 35 degrees at most. The high humidity is expected to make you sweat too. Slap on some sunscreen, put on a hat and a pair of sunglasses, and you're ready to go. An umbrella comes in handy too, just in case it rains.