The important thing to keep in mind is that permission to wear jeans to the office does not mean that it is a good idea to show up for work looking like you're there to do yard work.
|Not A Good Choice for Biz Cas Fri|
Unless, of course, you really are a lumberjack. In which case, you really don't need casual Fridays anyway.
For the sartorially conscious office worker, this is not an opportunity to become slovenly, but rather to stretch the genre a little bit. The key here is to keep in mind that in menswear, pants are the least attention-grabbing article of clothing.
Wear a conservatively cut pair of jeans (not baggy but also not of the overly slim type always worn by those vaguely suspect looking male models in the catalogs that you don't buy clothes from) in a moderately dark shade. It goes without saying that jeans for the office should not be overly faded, torn, or stained.
Pair these with a pair of brown or black dress shoes, preferably something a little on the older or more casual side. If you're the adventurous type when it comes to footwear, this can be the time to do something a little off the beaten track: suede loafers or colored oxfords. I'm a conservative bloke (and don't have the money to blow on lots of pairs of shoes) so I stick with my black McTavish brogues.
Top it off with a nice, open collared dress shirt. Sure, if you're the sporty kind of chum, you could wear a golf shirt instead, but I think that a good dress shirt makes a particularly good contrast against jeans. This fellow seems to be pulling the look off nicely:
|A princess and a guy like me...?|