Fitting hinges to a cabinet is a step that I find very nerve racking. You have a beautifully made door and an equally beautiful carcase which you want to join together using a hinge or two. In order to do this you have to cut into the door and carcase and risk ruining one of them. Here are a few steps which I learned at Waters and Acland which have helped me to become more confident at this.
Work out exactly where you want the hinge to be. Don't put them too near to a corner which you can't get your router into when doing the carcase.
Make a small jig so that you have a stable base for your router when routing out the hinges. Nothing complicated, just a hole in a piece of MDF and a couple of pieces on the underside to hold the platform in place.
Use a scapel and a hinge to mark on the edge of the door where the hinge is going to be. If you use the hinge to mark this out you can be sure that it's the correct size. Set a tite mark guage to be the depth of the hinge up to the centre of the pivot and mark this onto the door too. So you now have the position of the hinge marked out.
Set the depth of cut of your router to be slightly more than the thickness of the hinge plate. Clamp the jig in place over your marked out door and roughly cut the hinge slot out. How close you go to the lines depends on your confidence levels. It will save you time because it means that there is less to chisel out. But if you go over one of the lines....
Use a sharp chisel to cut out the remaining wood back to your lines.
Bradle and pilot hole the screws. I always put in posidrive steel screws first and only replace them with brass screws as a very final step.