Here's a few divisibility rules to remember.

Any even number is divisible by 2.
Any number ending in 0 is divisible by 10 or 5.
Any number ending in 5 is divisible by 5.
If the sum of the digits of a number is divisible by 3, the number is divisible by 3.
If the last number digits of a number is divisible by 4, then the number is divisible by 4.
If the sum of the digits of a number is divisible by 9, the number is divisible by 9.
If a number is divisible by both 2 and 3, it is divisible by 6.