Lay out the division problem in the long division format. Draw a two-sided box. Write the dividend -- the number being divided -- in the box. Write the divisor -- the number used to divide the dividend -- outside the line to the left.
Divide the left-most digit of the dividend by the divisor.
Write the number of times the divisor will go into the dividend on the quotient line, above the digit being divided.
Write the product under the digit(s) being divided. Subtract from the dividend. The remainder should be smaller than the divisor. Write the next digit in the dividend to the right of the remainder.
Repeat steps three and four until all the digits in the dividend have been divided and you have reached the point where there is no remainder, or there is a remainder smaller than the divisor.
Putting it all together with an example.
Divide 628 by 4.
4 goes into 6 once with a remainder 2. Write 1 on the quotient line.
Write the next digit (2) to the right of the remainder -- which makes 22.
Divide 22 by 4.
4 goes into 22 five times with a remainder 2. Write 5 on the quotient line.
Write the next digit in (8) to the right of the remainder -- which makes 28.
4 goes into 28 seven times with no remainder. Write 7 on the quotient line.
The final answer is 157.