For example: 15te-12he+10ty-8hy
First you group them into two binomials: (15te-12he) + (10ty-8hy)
Then find the GCF of each binomial: 3e(5t-4h)+2y(5t-4h)
And you'll notice there are now two terms and two similar binomials.
Combine the two terms into one binomial: (3e+2y)
Write the similar binomials into one: (5t-4h)
Then the factors are (3e+2y) and (5t-4h).