Charles Bishop writes:

What's the best way?

What species of metal?

Wide selection of bits he

http://www.use-enco.com/CGI/INSRAR?PMSECT=0000000606

Use a center punch to start the hole.

Use cutting oil and the right bit rotational speed.

Use a drill press if you have one. A good drill press will have a stop
setting to get the countersink depth just right.

Your screws probably use a 60 degree included angle.