Patterns
So much of math is patterns, from finding easy tricks for memorizing times tables to recognizing special products in algebra.
The first step of patterns is noticing repetition and being able to make predictions based on that repetition.
Some patterns are very simple. Some patterns are very complex.
For young students, start with simple graphical patterns. What comes first? What comes next? What do you think comes after that?
For older students, start to introduce math into patterns. Add numbers, or multiply them and see if students can find the patterns in the numbers.
See the lesson on Sequences for much more complex patterns.