Factoring is FOIL in reverse, in most cases. The main hint I can give you is if you have only 2 terms, for example x^2 - 4, IT HAS TO BE A NEGATIVE IN ORDER TO FACTOR. It will not work for positive.
x^2 - 4 factored is (x - 2)(x + 2).
If there are 3 terms, you need to look at the middle term and factor the other terms in such a way that the numbers can equal it.
x^2 - 5x + 6
to get the 5x in the middle you need to see taht the factors of 6 are 2*3 added together they total 5.
(x - 3)(x - 2)
Hope this helps.