It really depends on you and your body. You will have to experiment with what works for you. At the beginning, go for too much clothes because you can take them off as you run.
A rule of thumb that I have heard is to dress for 20 degrees warmer. If its 20 degrees out dress for how you would if you were outside in 40 degree weather.
This is what I would recommend:
- A good running hat that wicks or a headband that will cover your ears.
- Running tights or pants. I like loose fitting pants that I can put tights under on the coldest days.
-Lightweight gloves (I personally use the $1 gloves from Target, but you can get wicking ones.)
- A good mid-weight jacket. It should zip up to cover your neck at the beginning of the run. Some jackets have thumb holes so that the sleeves act as pseudo-gloves.
- T-shirts (long and short sleeved) that are wicking. Do not run in cotton. It just holds the moisture in.
- good thick socks. In the winter, since I am wearing pants, I often wear regular socks instead of running socks because they cover more of the leg.
Have fun in your running group. That's where I met many of my good friends.