Dog does not walk straight. What's the strategy to fix this?

My 2 year old mutt does not walk straight. He keeps changing directions and walks zig-zag. He has no sense of direction and would even try to circle around the same spot because of some smell probably. Also he would tend to run when being walked and i have to pull the leash. I want him to walk at the speed that i do and to not change direction on own. He seems to forget that he is on leash and will try to run hard only to be pulled back. How to fix this?