Break the numbers of the equation into smaller, more manageable chunks. For example, if the equation is 24 x 13, break it up as follows: (20 x 13) + (4 x 13). Break it up into the chunks of your choice, but make the chunks as simple as possible. Use round numbers or numbers that end in 0 or 5, as the multiplications of these will be easiest.
Solve the two chunks of the equation. 20 x 13 = 260 and 4 x 13 = 52.
Add the two answers together. 260 + 52 = 312, which is the same answer to original equation: 24 x 13 = 312.