It looks like you're off to a good start, but I'd definitely invest in some kind of portable folding reflector if you're going to keep doing natural-light portraits. The last one there with the young blond man could really use some sparkle from a fill light to open up his face and particularly his eyes. If you have a flash (something manual like a Vivitar 283/285 would be more than adequate for the cameras you're using), I'd learn to use fill-flash as well. Typically you'd set the fill flash to one stop less than the ambient light (ie if your meter reads f11@ 1/60th, you'd set the flash to f8). If you have a flash, post what kind it is and we (the APUG collective) can provide input on how to accomplish this with your flash.