I'm new to head shaving myself, What i did on the back of my head is run your other hand infront of the razor and feel your way. You can feel the stubble that you missed. as far as the razor burn, Try going With the grain for your first 3-4 shaves to let your scalp get used to the friction. make sure you are using a good shaving cream or oil to cut down on friction and razor burn.
Also try going as slow as possible, try to avoid going over the same place too many times. I'm at a slight advantage because i used to buzz cut my own hair for years, so i got good at Feeling with my head where i have been and where i havent, think of it like mowing the lawn