Portraits/Expressions

I think that with both headshots you've posted you've shown that you already have an eye for framing. I think that both look like very nice natural light portraits. I think you have already identified your biggest problem which is sharpness.

You'll typically see a lens, especially cheaper lenses, get sharper as you stop them down to about half way. I'm guessing that your lens hits f6 ish at 400mm, which means you're stopping down to f9 or more to get it sharper. Higher ISO might help you get there, but with an older camera you'll want to play around with the ISO to see when you get too much noise.

Part of your sharpness problem may also be your shutter speed. Rule of thumb is that you want your shutter speed to be double the focal length for hand held shots (I'm assuming you did this hand held). You shot at 1/160, but this rule of thumb would suggest you should have shot at 1/800, which is obviously hard to hit when you are limited by your aperture.

Your lens can hit f4.5 at 100mm which is still a great focal length for portraits. I'd suggest playing around with 100mm, stopping down to f6, and trying to get your shutter speed a little higher (maybe ISO 400, doubt that would be too noisy). You'll probably get sharper images that way.