When I was 15 I took my first art class in high school. To get in the class I had to present some of the work I had done on my own at home so the teacher could see where my skill level was at. I presented a large portrait of a musician in a band I liked. She praised my work. Then when the class started I was informed I was doing it all wrong. Up until that point I had always drawn things by gaging angles and distance. When we started doing portraits in class I was introduced to proportional grids. This is what we were taught. This is what we were expected to do. This is what we were being graded on. And on and on this went as a red thread in every art class I took, every book I bought for the next 27 years.
I'm not saying don't learn this method. I'm saying learn it and break this rule as fast and often as possible. The late and great Andrew Loomis has a series of drawing books you can get as a free pdf download. Learn it, know it, do something else. Here's why:
I drew the sketch above a few minutes ago. It is a very generic example of a face you can get drawing a proportional grid. The problem with drawing this way is that your brain switches to this mode of drawing symbolically instead of drawing what is really there. So you end up trying to draw the grid instead of your subject. Not to mention that unless you are a 20-40 year old white person of averge weight, your face won't fit this grid anyway. I won't even mention the part where it takes so much time to get the grid drawn, then you draw your portrait and getting it looking nice, then you have to ruin your drawing trying to erase your grid. Oh wait, I just did.
Young white women are the most common drawing subjects for portraits among beginners. Once you start branching away from that and learning to draw other ethnicities and age groups you realize their proportions range greatly. I don't even have the same face I had 10 years ago. So what do we do to fix this problem? Learn to draw lights and darks.
Below are a series of sketches I did very quickly. I spent less than a minute on each. They are the first pass of blocking-in a portrait using techniques I learned from Jonathan Hardesty's Essentials of Realism class. In this class we learned the best way to block in a portrait it to loosely measure your angles using areas of light and dark as a guide. So instead of drawing a face or an eye you draw the highlights and the shadows around it. Doing this allows you to block a portrait or entire scene in very quickly, then you make passes tightening it up. They may not look like much, but the thing I thought was really cool is that just by doing this you get the placement down lightening fast and already the sketches look like each other. This is very exciting for someone like me, who does sequential art and struggles with getting my characters to look the same in every frame. As an added bonus, you also start paying more attention to the value structure in your subjects. I won't even mention the time saved not having to block in a stupid grid. Oh wait..
The next drawing I did of Marlene Dietrich. I did about 3 passes tightening things up. It's easier, at first, to do subjects that have a lot of contrast in them. Start by drawing the shadow shapes. Group everything into dark. light and midtone. Let your darks and lights describe your forms. Remember to squint and let your color ranges group together. This takes practice but it's very worth it. You are training yourself to see things differently. Once you get the hang of this then you can move to subjects with less contrast. In some cases the lessons you learned drawing constructively (using a grid to draw contours) will actually come in handy on subjects with few or no shadows on their faces. Still it is a good idea to think of drawing your subject by edge shapes, no matter how vague they may be, in order to keep your brain from drawing symbolically.
I wanted to point out that even though I used portraits as subject matter this method can be used to draw anything. I urge you to try it. If people aren't your thing try a still life. I also urge you to check out Jonathan Hardesty's class on Schoolism. If free is more in your budget or you want to get a preview of what to expect then you can check out his channel on Twitch.