Most of those ^^^^ helpful replies come from people that know what they are talking about. My own approach as an aspirational amateur for whom portraiture holds attraction (and I've been having a go for years) is twofold. First, I look at portraits from photographers I admire and like, I try to find what it is about them that attracts me and observe how their photography adapts and changes. I work on how to replicate that, which helps build technical competence (mebbe ; ) ) I then have tried to develop my own style to "say" something from the photograph, to make it more than a snap of a face.
Curiously, I have significant prosopognisia (face blindness), I would struggle to identify a person in real life from their photo which probably strongly influences the way I approach the subject.
One of my long term influences is David Bailey, here's the sort of thing I mean.
The classic Jean Shrimpton image
<this space might have been a scan of a 40 year old print of a very early attempt at portrait inspired by this, but I decided it was just too not good>
And here is a scan of a print of some work my daughter did with me when she was doing her A level 14 years ago), where I was advocating the "try to copy" approach, I think for all the technical issues she did a credible job as a beginner. (OK, with substantial assistance, but even so)
I think that's not a bad fist at capturing some of the spirit of the Shrimpton image style.
And then, here's my own work. First up, David Bailey inspired by David Bailey
Available light, a very hasty set up grabbing an opportunity I had (courtesy of those nice guys at Olympus who had a long standing relationship with him)
And then Ray Frensham, an official Bohemian eccentric. You can then see the link from that (and other images from Baily, Mario Testino and the like) to the sort of work I feel I've done is halfway decent,
I'm only too aware of the technical shortcomings, but then these pictures are only for my own amusement, just because the focus is off what I might want, or maybe a shadow is too harsh and could have done with a fill in reflector, doesn't mean I won't get paid, so that's OK.
Basically, work out whose images you like and admire, work out what you like about them, work out how to copy them (which is where you'll develop the technical skills) and make pictures. Keep 'em all. Some you'll like, some you won't but it's fun to see the journey. It's easy now you don't have to store negatives. Have fun.