Like the others said, even stitches and tension come with practice. So do it! Gives you an excuse to knit more.
I've heard that the slip knot (it is a true slip knot?) should have the loose, `slippy' end on the tail, so you can adjust the tension on it. If it doesn't move, you mave have yanked the knot itself too tightly, or actually doing another kind of knot.
End stitches are notorious for being loose. I thought there was a sticky for this topic, but it usually comes up once a week or so. Do a search in the How To and/or General forums for `end stitch'. There's several ways to remedy this.
Finally, yes, everyone was was like this in the beginning. Like I said, practice, practice, practice!