A good pair of running tights makes all the difference in cold or wet conditions. The extra coverage and compression that they offer helps you warm up more quickly (very important if you’re struggling to motivate yourself to leave the house!) and reduces the likelihood of your suffering a muscle injury.
Running tights come in different thicknesses, depending on how adverse the weather conditions. Look out too for products that are designed specifically for trail running, or ultra light versions for racing. Some will also have small key pockets for storing items as you run. Men’s and women’s tights are cut differently.