Like as has been said before, ride on the pedals, ie. keep most of your weight on them most of the time, lift your bum off the saddle when going over rough patches, don't ride through potholes.
Use a low/comfortable gear to start with, until you are used to riding again. Do not use a gear that you have to push hard on, you'll get plenty of that when you meet the hills.
Don't be tempted to ride too far, always come back home thinking you could have gone further. Try 5 miles first, a week of doing that, then try 10 miles for the next week, when you are comfortable with that, increase by 10 miles per week, until you feel you have reached a plateau. Stay at that level until you know you can do more.
Eat wisely, carbos are what gets used in your muscles, (rice & pasta are good). Take a drink, preferably water or an isotonic. & drink it, don't return home with it, or you will dehydrate yourself.
All the best.
PS If you can get hold of an old turbo trainer, you can keep getting fit even if it snows outside, they are much under rated, until you have used one.