These are generalities, and others will leap in with counterexamples, no doubt -- sometimes it's a happy combination of elements rather than a mere assortment of features. But these characteristics are fairly conducive to upwind sailing:
* Sloop rig with high-aspect, powerhead mainsail and/or full battens.
* Large overlapping headsail, either fractional or masthead. A good genoa supplies much of your drive to windward. Ability to sheet headsail in tightly, or at least control the slot.
* Long waterline, narrow beam. Some people subscribe to a v-shaped keel for added lateral resistance, others prefer some kind of hard chine.
* High ballast ratios to keep the boat somewhat upright and reduce leeway.
* Fin keel with NACA foil profile: the deeper and narrower the better. Deep narrow fins w/ bulbs is the trend.
* Spade rudder, likewise a lifting foil. Possibly dual rudders to keep the foil vertical when heeled.
* Perhaps non-intuitive: slow boats may point better than fast ones. A fast boat moves the apparent wind onto the nose and must sail wider angles. A slow boat's apparent wind is closer to the true wind and it should point higher. The old 12m boats were paragons of pointing, but they were much slower than an Open 70, speed-over-ground. Despite narrow hulls & flat sailing attitudes, fast multis often have trouble pointing above 60 degrees because their apparent may be 2x true wind speed.