I slightly changed my habits with the intention to change them more, but we still drive out to the far away mall or movies on weekends when we are bored!  Overall if we want to do something, we aren't going to NOT go just because of Gas. 

However here are some of the most obvious tip, but this is what I do:

1. Before you leave the house for one thing, sit and think about anything else you need while your out.  Plan your route accordingly.  I already do this on the way home from work every day, but I have recently decided to *try* to do this even if we are going to a movie or dinner.  Basically, I'm trying to make each trip count for as much as it can.  The worst feeling is when you get home and realize you have to go out again for one thing.
2. If the purchase, item, etc, can wait - let it wait.  Wait until you have a dozen things to buy from the store instead of running just to get one thing.  We used to go grocery shopping on a whim, whenever we needed something.  Now we make a list and try to get everything at once.
3. If your husband has a more gas friendly car, make him drive everywhere ;)
4. You got legs - use them!  I told my husband this summer we won't be hopping in the car just for slurpees.  We'll walk, it's only about a mile round trip.  Last summer we walked half the time but got lazy the other half.

And don't forget to start carrying more cash around!  A lot of gas stations are now charging more for Credit Card users, and if you haven't seen that on the news, it's likely you didn't even notice.