the way I do it, the 1x2 is key so I will U U U till I get it matching my f2l. if I dont have a 1x2, I look to see if corners are solved with U, U', U2. if yes, do the edge perm, cube is solved. (theres only 4 edge only perms) if not I will look at how many edges are positioned and how many are not. I have a branching system of PLL's. basically there are perms that move 2 edgies and 2 corners, 3 corners, 3 edgies, 3corners and 3 edgies, 4 corners, 4 edgies. six branches. you can make up your own system. I am learning g perms last cause I just 3 edge + 3corner algs back to back. but what I mean is the 2+2 is easy to see cause when you have 2 opposite edges solved you already know its a 2+2 perm. there is no other way. when you have two neighboring edgies you can usually just U U U till you get a three edge perm.