Funzzle's medium Sudoku starts with 30 to 32 numbers. Singles get you far, but almost every grid needs at least one pointing pair: a digit whose only places in a box line up in one row or column, which rules it out of the rest of that line. A new medium grid comes out every day.
Fewer givens (30–32 instead of 36–37) and at least one step where no single is available: you have to rule a digit out first, usually with a pointing pair, before the next single appears.
If a digit's only possible cells in a 3×3 box are in the same row (or column), the digit must go in that row inside the box, so you can remove it from the rest of that row outside the box. The coach highlights these when you ask for a hint.
It helps. Pencil marks (notes) make pointing pairs easy to spot. Turn on notes mode and the board keeps them tidy as you place digits.
On Sunday, Tuesday and Wednesday. This page has a medium grid every day.