Here are some suggestions to fill in the blanks:

1. **skating**
2. **important**
3. **with**
4. **place**

The completed text would read:

"A favourite winter activity is (1) **skating**. But before you go skating on a pond or lake, there are a (2) **important** safety tips you should know. The ice should be at least 6 inches thick. Never skate alone. Never assume the ice is safe, and do not go out onto the ice after an animal or toy. Always be familiar (3) **with** the area where you want to skate, and be sure it is well-lit if you go skating at night. The safest (4) **place** to go skating is on a skating rink. Some cities have outdoor skating rinks. And"