One thing to keep in mind is that dovetails do not need to be very deep at all. Some sights come with bases that are WAY too thick. So the first thing I do is file the base of the sight so it is fairly thin. When I use the hacksaw, I only go down about the depth of the teeth on the blade.
It can be a unnerving doing your first dovetail, but if done slowly and cautiously, it's not too bad.
Here's a few pics from installing a rear peep with a dovetail base.
1st notice how thin the dovetail base is:
After marking the dovetail location and proper width (does NOT include the dovetailed angles), I used the hacksaw to make a series of shallow cuts...as stated above, about the depth of the teeth on the blade.
After very carefully removing this area with a fine flat file, I used my "safe" triangle file (one side with the teeth ground off that rests on the already filed surface and won't cut down anymore, just an angle into the sides.) and cut small dovetail edges. Go slowly here. A few strokes on each end, then try your sight. A few more strokes, try the base. You'll get to a point where it will start to go in.
At this point, I'll use my brass drift and a small hammer and lightly tap to see if it will go in more. If not, I push it back out, take a couple more light strokes on each end with the safe file, then try again. I do put a very small drop of oil on the dovetail during this process. Eventually it will very snuggley fit with light tapping.