Jeans: fit is important, a nice taper and get a high enough rise, no superfluous stitching/details/rips, no funny fades/rinses just indigo dyed. Don’t have to be selvage but if you do a turn-up it’s looks neater than non-selvage, for cyclists an Edwin ED-55 is a good cut. Don’t go slouchy anti-fit. A decent belt that matches your shoes, not exactly but don’t go for black if you are wearing tan shoes.
Shoes: don’t let the side down with shite shoes, no pointy scuffed monstrosities a dark tan/brown brogue/oxford or even a suede loafer, don’t go for black office shoes, it will look like a dress down Friday in an accountants office.
Shirt, 3 important things, fit, fit and fit, not baggy or billowy round the waist, a proper fitting collar even if you don’t do the top button up, nothing worse than a wrong size collar spreading wide open. No silly double buttons at the collar, no logo’s no flowery prints. You can go slightly less formal with heavier weave cotton or linen.
Basically you can cover almost formal to casual by softening the fabrics (suede/linen/soft cotton through to polished oxfords/crisp shirt etc or a mix but it goes wrong if you try to pair ultra formal with sloppy casual)
Whatever you do, don’t ignore the shoes, and if you want to go snazzy with colour only do t with one item, so those bright patterned socks are fine just don’t do the same with the shirt.
If you get it right you will look better than most as uk men do not dress well and 99% look like a sack of shite.
If you get it wrong nobody will notice for the reason above.