Looking at your profile, I am pretty sure this is a self-portrait. As everyone else has said, they're tricky, because composition and fine-tuning are both far, far harder!
However, I will confine myself to a couple of things on the purely technical side.
First, the choice of the long end of your zoom is spot on. Just right for this sort of shot, though you could go even longer if you have a longer lens!
The ISO, aperture and the mode, along with the fact that the camera flash fired suggest that this relied on the camera flash, and that would explain an awful lot of things. There's a second catchlight, so you may well have had another flash off-camera - I'm guessing it also was a fairly small gun, and didn't have a brolly or soft box on it..
It's nto a good or flattering light source: depsite the fact that you are a good model, and have posed well. That's a lovely wistful look you've got there, and I wish you'd been in front of my camera!
For most women, softer light is better and more flattering, most of the time. Diffusing a flash (even by bouncing it off a white wall or ceiling) improves the quality, but reduces the power. This is why I always use either mains-powered studio flash, or natural light for this kind of shot. Flash units are cheaper than they were, but not trivial - a very basic outfit is a couple of hundred quid.
So natural light is a good option - or find another tog who has studio gear, and tag along for a session. That will get you right up to speed on all sorts of details. It's a struggle otherwise.
But... If you go it alone, aim to shoot around f/8 to f/16, at 100 or 200 ISO (This can be problematical to achieve, given that basic flash units lack power. You may need to see how high you can take the ISO before you lose quality.). Go for full manual control, and a plain background that won't need work in PS. Black can be good, and shows up colours really well.
Or use natural light, and a wide aperture, possibly with a very high ISO setting to give a grainy result?