Winter is not necessarily a time to get sick...it's just a common time for the flu. You can do a lot to keep your baby healthy.
1. BREASTFEED! If you can, of course. I strongly encourage it...it will provide your baby with LOTS of added immunity besides all of the other benefits to both you and your baby. My first child was sick a lot (bottle fed) and my second child (breastfed still at age 2, my own question coming later!) never had the flu, a cold, an ear infection, etc. She actually has a lot of health issues (lactose intolerance, Celiac disease, other digestive problems) so breastfeeding was absolutely the best I could do for her.
2. Keep a clean house. I think this is important regardless of how old your children are, but it's definitely one thing I can do to feel that I'm doing my best. Disinfect germy areas (phone, remote, doorknobs, etc) and just generally keep your house clean...you don't have to go overboard, but it's so nice to have a clean house! The best thing about a clean house is, if you start with a really clean house (i.e. before the baby comes) it's much easier to keep it clean by just spending 20 minutes a day. I really don't spend much time cleaning because I clean when it's already clean...wipe down the bathroom sink every morning, wipe the shower with your towel when you get out...walk around with a dust rag while you're on the phone, etc.
3. Limit certain contact. I don't follow the "keep your baby in" for X amount of time, but again, common sense is important here. Don't bring your baby around lots of other children (breeding grounds for germs and illness, just a fact) until she's a bit older, wipe handles of shopping carts, etc. Insist people wash their hands before holding your baby and don't feel bad about doing it.
4. Immunizations. I won't even get into the debate here, but immunizations are VERY important to keep not only your own child healthy, but others as well. No risks of autism, etc, have been proven from immunizations, so please don't let anyone scare you away from them (because there are certain people who will try, believe me.) Because of immunizations, we no longer have no deal with many childhood diseases. My oldest had pertussis (whooping cough) before she was immunized and it was very scary...at that point, I knew I would never turn down a tried and tested immunization for my children.
5. If someone's sick...no contact. Try to prevent getting your own self sick by eating well, getting enough rest, etc.
Congratulations!!