By bus: the bus over the causeway is the most popular means of getting on to the island, and although you can drive your own car over, there are expensive parking and entry fees. Either you can catch buses such as the 65 and 143 directly from Orchard road, the 61, 84, 143, 145 or 166 from Chinatown or the Sentosa bus C from Tiong Bahru MRT station.
Alternatively you can travel by taxi directly to the World Trade Centre (WTC) which is directly opposite the island and runs regular shuttle buses. The nearest MRT station is Tanjong Pagar, which is a short taxi ride away. On a weekend you can expect to wait for up to 30 minutes at either end of the shuttle, but the journey is quick and it stops at various points on the island.