Set the distance to the longest setting. Cut the hair on top of your head. You might have to make several passes to get all the hairs. Use a mirror.
Set the distance to the middle setting (halfway between longest and shortest). Cut the hair on the sides and back of your head. Cut by placing the cutting part at the bottom of your hair pointing up and moving it upwards. When the trimmer approaches the top of your head (where you already cut), lift it gradually so that you get a smooth transition from middle to long length hair. Use two more or less parallel mirrors, eg the two mirrored doors of a bathroom cabinet.
Remove the distance part from the trimmer entirely. Cut the hairs on the back of your neck. Again use an upwards movement with the trimmer. Make sure that the top of what you cut is a straight line. Forming the straight line at the bottom of your hair is the point of this step.
Put the distance part back on and set it to the shortest setting. Do your sideburns and bottom of the back of your head. Start lifting the trimmer to transition almost immediately on the backside and just above your ear on the sides. Cut the hair behind your ears by running the trimmer backwards along the top of your ear, with the lower edge pressed against the ear base and the upper edge in the air.
Shower/​rinse off the cut hair. Take a last pass with the trimmer or a pair of scissors on any hairs you may have missed.
Maybe a long shot, but does anyone know of a good way to give oneself a haircut?
Get a hair trimmer.
Set the distance to the longest setting. Cut the hair on top of your head. You might have to make several passes to get all the hairs. Use a mirror.
Set the distance to the middle setting (halfway between longest and shortest). Cut the hair on the sides and back of your head. Cut by placing the cutting part at the bottom of your hair pointing up and moving it upwards. When the trimmer approaches the top of your head (where you already cut), lift it gradually so that you get a smooth transition from middle to long length hair. Use two more or less parallel mirrors, eg the two mirrored doors of a bathroom cabinet.
Remove the distance part from the trimmer entirely. Cut the hairs on the back of your neck. Again use an upwards movement with the trimmer. Make sure that the top of what you cut is a straight line. Forming the straight line at the bottom of your hair is the point of this step.
Put the distance part back on and set it to the shortest setting. Do your sideburns and bottom of the back of your head. Start lifting the trimmer to transition almost immediately on the backside and just above your ear on the sides. Cut the hair behind your ears by running the trimmer backwards along the top of your ear, with the lower edge pressed against the ear base and the upper edge in the air.
Shower/​rinse off the cut hair. Take a last pass with the trimmer or a pair of scissors on any hairs you may have missed.
This is basically how I cut my hair too.