细水长流 A thin stream flows long. To keep at something steadily, or to plan carefully so that resources last.
放长线钓大鱼 Let out a long line to catch a big fish. To plan for the long term in order to gain more. The Handian dictionary adds that such a plan “cannot pay off at once.”
来日方长 The days to come are long. There is still a long time ahead. The Handian dictionary cites a letter by the Song official Wen Tianxiang as an example.