I love these two looks when they are done with subtlety. Preppy on the one hand can be updated by making sure those khaki pants are well fitted, with the right waist, length and style of cuff. When this look is worn oversized and sloppy, it just looks old and dated. When it's trim and very subtle (not screaming hey look at me, I'm preppy), it can look fresh. On the streets of Nantucket you see this a lot. It's a club, if you are a 'club' person, join, if not, do your own thing. Michelle Obama does it fabulously. It's that great button down cardigan that we love!
Trendy is another look that can look great when done quietly. Good shoes, good trouser, white shirt and a bang up earring or necklace will say it all.
Really all very simple, less is more.