To be honest, I'm hard-pressed to think of what couldn't be improved. The first thing that I notice is the background; stained concrete block, standing in what looks like a dirty alley-way. I'm sorry, but that does NOT scream pin-up to me at all. As mentioned the lighting is very harsh and the fact that your shutter-speed was 1/800 tells me that you didn't use any sort of off-camera flash, which both of these images desparately need. If you are going to use a linear background like bricks, please ensure that they're level. The pose has been mentioned, but the clothing choices are NOT appropriate; what sort of pre-shoot consultation took place? A white & dark blue dress? You've probably got seven stops of range right there so very much less than ideal, the dress doesn't look like it's seen an iron in a very long time, and how are pink shoes appropriate w/ dark blue? Not on any colour wheel I can find.
The second image is much better, but still lacking. The top of the dress is blown or nearly so in places, and the specular highlights on her knees are overly strong.
Being a good photographer is all about the details. Anyone can come along wtih a camera set to 'Auto' and take some pictures. You should be capturing photographs. That means taking care of the details; ensuring that clothing choice is appropriate (yes, I am well aware that despite how many times we might talk to a client about this, it sometimes goes wrong, c'est la vie), the clothes are neat and clean and ironed. It also means choosing appropriate venues. The second background is much more subtle and pleasing to the eye than the first.
Being a good photographer (as in good enough to earn pay) also means being able to deal wtih all sorts of conditions. Granted mid-day on a bright, sunny day is NOT the ideal time to have to shoot, but ehh... sometimes that's when you have to, so bring out the lights. One light with a large softbox, or even a large reflector would have made all the difference here.
These images aren't bad, but they have a long way to go to get where they should be as commissioned work.
Just my $00.02 worth - your mileage may vary.
~John