Great stuff.
One major thing you need to avoid are shadows. You really don't need to be using a flash outdoors. There's plenty of great lighting out there. Shoot in the afternoon around 3 pm. Flash gives too much of a fill light effect. You lose texture in the skin and also can make the image look terribly flat.
If you must use your flash, haha.... You should look into an omnibounce or a demb white card. It makes the flash less harsh and bounces light in all directions. This is all assuming you really dont wanna spend a whole lot of money. If you do, you should grab a flash stand and an umbrella, shoot from above. You can also look into a few lighting/studio kits so you can have a few options where you want the light coming from. You can also experiment with bedsheets to give a cheap soft box effect.