Write the decimal out on paper. It's easier to do math problems, especially converting decimals into fractions, if you write the problem out.
Change the decimal into a fraction. The numbers to the right of a decimal point in a positive decimal and to the left of a decimal point in a negative decimal are fractions with denominators of only 10, 100, 1000, 10000 and so on. For example, 0.50 is actually 50/100, and 0.849 is actually 849/1000. Keep any numbers outside the decimal point to the outside of the fraction. For example, change 1.25 into 1 and 25/100, without the 'and.'
Simplify the fraction into the lowest terms. For example, 50/100 would reduce to 1/2 because both numbers are divisible by 50, and 1 25/100 would reduce to 1 and 1/4, without the 'and.'