How to hold the razor
Place your fingers over the razor as shown in the picture below, with your forefinger and middle finger on the left side of the scales, and your ring finger on the right side of the scales, keeping your thumb to the left, and placing it on the shank/jimps of the razor.
For more information on how to hold a straight razor, please consult this page.
The importance of blade angle
Simply put, it's all in the angle. If the blade is flat against your face, it will not cut your beard, and if at a 90 degree angle, it'll likely cut more of you than your beard! Ideally you want about a 30 degree angle, however it can vary based on different razors and such. The easiest way to determine the proper angle, is to put the razor nearly flat against your face, near your sideburn at the top of your cheek, and as you slide the razor down your face, slowly tilt the razor away from you (while keeping contact with your face) and at a certain point you'll feel and hear the hairs shave right off. It's this angle that you want to keep for the majority of your face/neck. In some areas, you can tilt the razor back a little more (which will cause the razor to "bite in" at the hairs more aggressively) to get a little more aggressive, which is the beauty of the straight razor shave, and why they can deliver the closest shave, as unlike a DE or a cartridge razor that has a "fixed" angle, the entire time you are shaving with a straight razor, the angle is constantly changing based on what works best for YOUR face. It's the ULTIMATE adjustable razor!