In the winter, it gets pretty cold; here are some tips for winter riding habits. For your horses, you should definitely put on a quarter sheet before you ride-at least while warming up your horse. This keeps them partially covered and helps them keep warmer, and also improves durability. It can also be removed easily once you have warmed up.
Another good winter habit is warming your bit a little before putting it into your horse's mouth. I know I would not like a freezing cold, hard piece of metal forced into my mouth in the winter. To warm up your bit, you can rub it between your hands-I suggest having gloves on for this- and/or putting it under warm water for a few seconds. This is definitely more comfortable for the horse and a good tip to keep in mind.
For the rider, wearing gloves is always a good idea. I know from experience that tacking and grooming a horse without gloves in the winter is PAINFUL. Wearing a big, warm winter coat is a must as well. If you're without a proper coat, it will leave you very cold when riding and that makes you stiff and your horse will pick up that tension. You can always take off your coat once you've warmed up a bit from riding around. I also like to wear under armor underneath my numerous layers of clothing. Thick socks are good, too, I know my toes get frozen when I ride sometimes.
And lastly, before dismounting, walk around on a loose rein. Kick your feet out of the stirrups, and wiggle your toes and ankles around for at least two laps. If you just come to a halt and try to dismount without walking around for a bit, it will hurt your toes and ankles and feet SO badly when you try to dismount. So walk around for a little, wiggle your toes and ankles, and come to a halt and slowly and carefully dismount, making sure you bend your knees on the way down. If you keep in mind these tips, you'll always have a fun, safe, and hopefully warmer ride despite the chilliness outside. :)