Børge, I think you are doing a fine job though there are some things I can see that I think would help improve your portraits.
In the first picture I see that you are using cross lighting with a soft key light to camera right and a hard fill light to camera left. This is making for competing hard and soft shadows across her body. The fill light on the left is also positioned low enough that the shadows it is creating are going upwards across her face. Raising the fill light would help, softening the fill light with a larger modifier would help more. Not only that I would suggest experimenting with the position of your fill light and try it on camera axis, if you must use a bare speed light or small modifier for fill try it as close to the lens as possible, if you have a big umbrella try it just above or behind the camera. Also the key is spilling a good amount of light onto the ground as well as the tree behind the girl so feathering the key upwards and more towards the camera position, instead of pointing it straight at the model, would help to reduce this and give better subject to background separation.
The second picture looks like just one hard light source to the left with ambient light as your fill light? I think it could be improved with a softer light source, raised a little bit. What are you using for light modifiers? Are the blown highlights you're finding the shine on the skin or are your lights turned up to much?
I find speed lights limiting in their power output for this sort of work, not all soft light is created equal and unless you're one of those guys who likes shoving 3 or 4 speed lights into one large softbox they just don't have the power to keep up with the larger strobes. They are small and have their benefits, but a battery powered strobe or two shouldn't take much longer to set up and will give yo much more versatility with not only having more power but also more choice of modifiers.
