How do you find the next number in a given sequence?

First, you look for the difference between every number in the sequence, ie. what do you add to the first number to equal the second number? If you find that the difference is the same for every number, then you just add that difference to the last given number in the sequence to find the next number. If the difference between each number is not the same, look for a pattern in the differences (eg. goes up in odd numbers/adds multiples of 2) then repeat this pattern in order to find the next number in the sequence.