I use a grid method to get tough subjects, specifically portraits of people & wildlife looking right. If you're painting someone you want them to look like them...just like if I'm painting a finch...I want it to look like a finch, not a warbler.
I just make a grid on both my sketchbook or canvas and on the reference I'm using.
Then I draw a line drawing, each square at a time. When I'm done, I remove or paint over the grid lines. This little guy was featured in one of the classes I teach. (Those of you in KY who took this class will remember this little guy.)
Are there other ways to do this? Yep. Are there better ways to do this? Maybe, probably. But when I don't have the option of "taking liberties" with a subject, I use photo references. In art school, this was not allowed in my initial drawing classes....for good reason. I needed to do the work so I could get better as an artist. Now that I'm teaching and selling my work. If I have a reference, I use it.