The first thing I check on any pair of khaki trousers is the shade. Khaki isn't one colour, it's about six, from a pale greige that reads almost beige to a proper mossy green, and the one you pick changes what it does in your wardrobe. Too yellow and it fights with everything, too green and it starts acting like a statement piece when really you want it behaving itself.
Fit is where most people, me included, get caught out. Khaki trousers come from the chino and utility world, so they're often cut generously through the hip and thigh and then taper in hard at the ankle, which is fine if your thighs and ankles agree on proportion and less fine if they don't. Try them sitting down before you decide, because a waistband that's comfortable standing in a shop can dig in the second you're at a desk or in a car for an hour. If you're between sizes, go up rather than down, a slightly looser khaki trouser still looks deliberate, a tight one just looks like a decision you regretted at the till. Length matters more than you'd expect too, a proper break at the shoe makes them look like trousers, no break at all can tip into cropped territory by accident. On pairing, this is where khaki earns its reputation for being easy without actually being boring. A plain white t-shirt and trainers is the obvious one and it works because the khaki does all the personality and the top does none. A fine knit in navy or oatmeal with loafers takes them into an office that doesn't require a suit. A denim shirt on top sounds like it shouldn't work, two workwear fabrics together, but it does, because the colours sit miles apart. I've worn the same pair with a black roll neck in winter and a linen shirt in summer and they didn't look like they belonged to two different outfits, which is more than I can say for most trousers I own.
If you've got none and you're starting with one, go for a straight leg in that mid tone khaki, not too pale, not too green, with a bit of structure to the fabric rather than anything soft and drapey. It's the version that goes under a jumper in October and under a shirt in May without either look feeling like a stretch. Stand in front of the mirror and ask yourself if you can sit down in them for a whole train journey without wanting to undo the button. If the answer's yes, that's the one.
