Hip to be Square

Pulling off a pocket square as a young professional without it seeming like a affectation is difficult.  I think a big part of making it work is making sure that your square doesn't compete for attention with your tie or shirt, (or jacket) and making sure your fold is neat and discrete.  Lastly--wear it comfortably.  If you seem nervous about wearing a pocket square, your colleagues will sense your apprehension and look wearily at your square.  Act like your square is just as much a part of your outfit as your shirt and all anyone will think about your square is that its just one element of a well put together look.

Make you're squares are well pressed.  They'll fold better and look neater that way.  I think a basic white linen square is the safest place to start, but also the most formal.  After that, I would suggest to pick up squares in a variety of colors and classic patterns, like madras, gingham, floral prints, etc. Stick with cotton and linen though--these materials don't have the flash that silk does, which usually something to avoid.  It also provides some texture contrast to a silk tie.

If you're not sure how to start wearing a square, I'd recommend a navy blazer--its plain, generally needs something to spice it up, and goes with any color or pattern square.  Unlike a suit or patterned sport coat, a blazer actually seems like it needs a square, and the effect is actually to be more sporty, rather than formal.  Stick with a solid shirt and tie, and your choice of square patterns is wide open.  Make sure the colors of the square coordinate with, but not match, the shirt and tie.  If you're sticking with a white linen square, then you can wear any shirt and tie you want.  Get comfortable wearing squares first, and start getting more adventurous with your shirt/tie/square combination second.

There are numerous online resources for how to fold a square.  Keep it basic at first--the TV fold, or standard three points--to avoid looking too much like a dandy.