At the risk of being absolutely contrarian with most of the board:
1) Never OCBD - it may be OK in the States.
2) I always wear jeans with tweed and odd jackets - or moleskin and much less likely, cord.
If I was to wear wool or flannel they would need to be plain front and be quite snug.
To me, loosely fitted formal trousers spoil the lines of the sports jacket and frankly do look dressed up in these days we live in.
I've always thought that jeans act as a sort of corset and flatter the male physique
with the jacket flattering the shoulders and chest - in fact jeans and sports jacket can be a killer combo.
3) Always spread collars, even cutaways, never regular or points. Spread collars give more space for the neck to move in all scenarios. Under a crewneck the collar sits perfectly and frames the neck. Any other collar squashes.
4) Always french cuffs. Why? Mine fold up perfectly with the cuff as a guide, to the elbow and take any shirt I buy from business to pub in 30 seconds, or starts up folded. I never wear shirts down to the wrist unless I have a jacket on. Why bother with barrel cuffs? With knots, you can still wear under a jumper - they don't really show.
5) Always crewneck jumpers, never V neck - and collars inside jumper always.