I am very confused about decreasing. I used to just k2tog no matter what, but I read somewhere that to make something look better you should use a left or right slanting procedure. After checking my knitting manual I am confused. On the left side of a cardigan for the neck shaping I am to decrease 1 st every row for ten rows. Would this be a left-slant dec or a right-slant dec? And would that be every row for that side or do I switch between them as I turn it around and knit back the other way?
Usually you do a left slant dec (ssk or skp) at the beg of a row and a k2tog at the end. The idea is to have them slant toward the center of the work. There are some more ‘designer’ style patterns that will have you do the opposite. Most of your decs are done on the RS rows, so I don’t know what you mean about turning and knitting the other way. If you’re working in garter stitch, the decs probably won’t show, so just use whichever you prefer.
[B]S[/B]SK, the “S” has that part that slants . That is the way your decreased row cuts across your knitted rows.
K[B]2[/B]tog, the “2” has the part that slants /. that is the way your decreased row cuts across your knitted rows.
Amy made an amazing photo illustration of increases and decreases here on this website. You can see how every kind of stitch looks. 
Decreases: http://www.knittinghelp.com/videos/decreases
Increases: http://www.knittinghelp.com/videos/increases