Remember a prime number has only 2 factors!
One method is increasing primes. In this method you divide the number by increasing prime numbers.
Example: 84=2•2•3•7
84÷2=42 42÷2=21 21÷3=7
There is the 2 factors method, where you keep writing numbers as a product of 2 factors.
Example: 84= 2•42
2•6•7
2•2•3•7
Then there is the factor tree, my favorite method.
Image from: schoolworkout.co.uk
Above is an example of a factor tree for the number 72. 72 is broken down into 2 factors, 9 and 8, then 9 and 8 are broken down into 2 factors, and so on, until the numbers that are left are the prime numbers. The numbers that are circled are the prime numbers.
Once you understand prime factorization you can explore GCF and LCM.
GCF
GCF(a,b)= the largest number that is a factor of both a and b
Example: GCF(7,14)=7
LCM
LCM(a,b)= the smallest number that is a multiple of both a and b
Example: LCM(3,5)=15
Check out methods for finding the GCF and LCM at http://www.purplemath.com/modules/lcm_gcf.htm
Then you can test out your skills at http://www.math-play.com/Factors-and-Multiples-Jeopardy/Factors-and-Multiples-Jeopardy.html