re: my ribbed scarf will never look professionally done =(
Yes it will.. ribbing is easy to learn, hard to master.
try smaller needles.. loose ribbing looks messy.. and smaller needles --RIBBING IS ALMOST ALWAYS DONE ON SMALLER NEEDLES ANYWAY--will help.. if the pattern suggest size 7 for body and size 5 for ribbing, try a size 4 for ribbing.
and remember, washing/blocking/wearing (repeat) will even out inconsistantcies.. old sweaters alway have perfect tension.. (but many an new sweater has some rowing out, or uneven ribbing!)
and stop being a perfectionist.. a good rib is better than avoiding ribbing, and after a few years of practice, a good rib becomes a very good rib indead!
Since it's for a scarf, the option to use smaller needles might not be a good one. You can practice on some waste yarn, but Sarah's advice is good, wrap the purl sts the opposite way and that tightens up the yarn. When you knit them on the other side, though, you'll have to knit through the back loop or the knits on that side will be twisted.