I stitch in 10-stitch wide columns working each 10-stitch row left to right and from the top down to the bottom of the page, then starting again at the top of the next column to the right. I park my threads using this method:
http://www.scarletquince.com/parking.php" target="_blank. I've tried doing it other ways but I find this method is the one that gives the neatest stitches because I'm not bringing the needle to the front of the fabric through holes that are already occupied by other stitches (doing so sometimes results in pulling the existing stitches to the front of the fabric and making them uneven, in my experience - especially on higher count fabric where the holes are a tighter fit).
I don't grid my fabric because I tried it once and hated it. I'm not counting any higher than 10 so I don't see the need for gridding and I've never miscounted as a result of not doing it. Other cross stitchers swear by gridding, but it's not for me. Just a matter of personal preference.
If you take a look at my Coniferous Forest in the SAL section you might get a better idea of what I mean. (I'm hoping to update it later today when Hubby's emailed me the photos).
Sorry, that all sounds a bit "me, me, me", but hopefully it'll make things a little clearer for you. Good luck!