A couple of things to think about regardless of the jig you are using.
First, make sure and mill a couple extra pieces of stock the same thickness as your work piece. You will need these to use as test pieces when setting up the jig. These need to be exactly the same thickness as your work piece or your set-up will be off.
Next, beware of tear-out. Tear-out happens when the router comes to the end of the board and the cutter tears the fibers instead of cutting through them. The best way to prevent this is to use a backer board, so the cut ends with the sacrificial board rather than the workpiece.
Another way to prevent this is to make a light back-climb cut on your first pass across the piece. This means you go in the “wrong” direction with the router.
This is a useful trick for keeping cuts clean, but make sure and make it a light pass. If you take off too much material when back-climbing you can loose control of the router, so go easy.
Of course it also helps to have a sharp router bit. With a sharp bit, a backing board, a light back-climb pass and a well adjusted jig you should be able to cut your joints with ease.
You can get more information about using routers with this link.
Now, how about trying to cut them by hand.
To the right is my first ever dovetail. I cut it with a chainsaw for a log home I was helping to build.
Does this count as being cut by hand? No jig, after all.