I need help with getting my dog to walk with me properly?

I know this should have been done a while back...but my dog is 3 and she just tugs so much when we are walking in the park. It's not to the point of intolerable, but I just want to know if there is something I can do to make it better. She tugs to the side, she wants to sniff the grass. Sometimes she tugs really hard. I guess the problem is that I used to have a huge yard and so we would play catch and then we moved to a different city and now we do daily walks. Advice please?