ok, so in the picture shown
what focus area mode, wide, spot or local?
if wide, then we really can not be sure that the camera hit the eyes
if local, then you had control of where the focal point was, was it on the eyes?
same with spot, if it was on spot then we would assume that the center of the image would be the sharpest spot, if you didn't' do the focus then recompose method
next, aperture
f5.6 is not a bad aperture to use however it's not the best either, they say the sharpest aperture on any given lens is f8, i can not confirm or deny this but I can say that at f8 you will have a better chance of getting the eyebrows in sharp focus when focusing on the eyes versus f5.6
i would have to assume this is more so when using the kit lens, there is nothing wrong with using that lens, just understand that you may have to use it at a smaller aperture to get the sharp results that you want. (also I am assuming you know that the bigger the f number the smaller the aperture, which means the less light coming into the camera, the smaller the number the greater depth of field, which is the more that is in focus, but you know all this already so I'll move on)
also it's good to understand that you need more light when using a smaller aperture, so f8 is going to require more light than f5.6 and light is what this is all about.
i can see you used the flash, on camera flash i am going to assume, 1/125th isn't the fastest shutter speed you can use with your camera, 1/160th i believe is the fastest you can get with the on camera flash on the a300. so 1/160th will give you a little better chance to freeze the subject, you may need to shoot in shutter priority mode or manual mode to get the camera to select that shutter speed.
another thing to think about is auto focus mode
single shot locks focus when you depress the shutter button down half way and will not change until you release and depress again
automatic will try to determine if your subject is moving and if the camera thinks the subject is moving it will try and keep the subject in focus
continuous mode camera will assume that you subject is moving and will continuously adjust focus to what it thinks it should be.
so understanding those modes of focus will help determine what mode you should be using for any given situation, in the above photo single focus i think would be appropriate, as they are probably not going to be moving too much
also it's possible to have your camera setup to release the shutter even if the camera hasn't locked focus, but i do not think that is the case.
also remember that every lens has a minimal focus distance, it could be inches or feet depending on the lens, so if you happen to be to close to your subject the lens itself may not be able to focus where you want. 0.38 meters(1.25 feet) on the 18-70mm
shooting in manual mode is going to give you better results in the end, it will take some effort on your part but in the end the pay off will be what you want. don't let the camera decide what is best for you. choose what focus area you want to use, choose the focus mode you want to use, choose the aperture you want and choose the shutter speed you think you will need, take a test shot and adjust from there, when using your flash remember you can control the output, so if you feel you need to crank down the aperture to f11 to get the sharp image but your photos are dark, crank the flash compensation up or better yet get a nice flash unit, but that can come later and should come later once you master the gear you already have. same with lenses, don't run and get a new lens until you understand what your lens IS capable of first. every lens has it's strengths and weaknesses.
and the most important piece of advice other than shoot tons of pictures is stop pixel peeping your images at 100%.
also understand that if shooting raw the images coming out of your camera will need some sharping applied to them, and i do hope you are shooting raw and learning how to process your images.
do you know how many photographers it takes to sharpen an image in post processing? One, and then there are 99 more telling you another way to do it. Sharpening is a whole subject by itself and one you should look into if you haven't already.
if not shooting raw then you are not using your camera the way it should be used, it's like buying Ferrari and not taking it out of first gear, same if you are shooting in Auto, manual mode will give you full control and you will learn how to use your camera.
as far as SSS on or off, leave it on until your shutter speeds hit 1/500th and above or shooting on a tripod, the a300 doesn't have MLU, mirror lock up, so turning it off while on a tripod may give better results in some situations but the mirror itself will give some vibrations so leaving it on may actually help with the a300 on a tripod, but this really depends on the tripod and if you are using a cable release or the timer, but that's a whole subject on it's own.
hopefully some of this post and others posts help you along your way, but do yourself a favor and have fun and don't worry about your images looking sharp at 100% view on your screen
so your latest photo may be the answer to all this, focus area wide, you are letting the camera decide where to focus, you need to be in control, so use spot or use local, spot is easiest to deal with, aim the spot at the eyes, hit shutter button half way down then recompose then hit shutter button the rest the way down, will see better results.
