I use the long tail without the slipknot, too, but if you prefer the look of having one, or it makes you more secure, then use one.
When I'm making a scarf that I want a bit of a decorative edge on, I slip the first as if to purl and knit the last on each row. There are different ways to do it, and as long as you're consistent, they're all ok.
When I'm not looking for a particular edge, I don't slip anything. As I knit or purl those first couple of stitches, I hold my yarn very taut and don't get a loose edge. Comes with practice, I guess.
I say don't focus on that one stitch that will be in the bottom corner. Keep going--you'll see how your stitches will get more and more even, as you go, and you'll get to practice on making the edge stitches tighter.