Start with the basics and go from there.   The key pieces you need to build a business casual wardrobe begin with a pair of flat front pants and a button-down shirt.  This uniform can be dressed up for a more classically corporate office with a sportcoat, tie and loafers or dressed down for a more casual environment with cool sneakers and a sweater.  The most important thing is that the pieces are well fitting and tailored for you. Additionally, having a dress code can make getting ready in the morning a whole lot easier.

The most important thing is to get a gauge on how other people are dressing and follow suit.   While jeans and sneakers may be the norm in many offices, for others that will never fly.  But no matter how casual the office, it is still a place of business and looking like you just rolled in from the gym doesn't ever work.   If you are able to wear more casual pieces to the office, they need to be neat and sleek.  Suede sneakers, a cashmere hoodie, a slim jogger, these can work very well for work as long as they fit well.  Same goes for denim; distressed ripped jeans and an old t-shirt should be relegated to weekend ware while dark denim and a soft sportcoat is a great choice for a casual type of office.