if you are using reduction, place all edges in the same slice (i.e. all solved edges in the U layer and D layer or R and L layer). then, for the first edge, find the 3 pieces that go together (slice them together just to make sure you dont need to flip a wing) then, BEFORE you slice them together, take the one edge you are NOT using to make the 3 group, replace it with a GOOD ALREADY SOLVED edge, slice the group together, replace your NEWLY MADE GROUP with the BAD EDGE that you moved out of the way, THEN restore the centers. this will solve 1 edge group, and leave the rest of the pairs undisturbed. with the last 3, sometimes you need to use this technique to make a semipair instead of a 3 group. after you make a semipair, a 3 group should be possible with 3 edges left. just use the aforementioned method. for the last 2 edges, you can use bigcubes.com to use the algs. or, you can learn a wing swap alg and the 4x4 OLL parity alg and solve any case with those 2 algs.