Firstly, does your dog think he is at Alton Towers, leaping all over the sofa, racing around, jumping and generally super excited whenever you get the lead out? If so, you will have little chance of control once you get outside. Start by getting the lead out and then putting it away several times a day until your dog is relaxed whenever it appears. Then work on not letting him out the door until he is in a calm state, this can take some time but it is worth it. Your dog will learn that unless he is calm he is going nowhere.
Follow the same procedure as you leave the house, have him sit and wait several times as you move out. If your dog strains to get ahead then do a sharp turn and walk the other way so that your dog learns that you are in charge and that pulling no longer works. Walk as though you are in control putting no tension on the lead, unless you need to correct your dog.
If you have a resistant puller there are some tools to help you. A Halti can work very well and most pet stores will help you with the right fit. You won't need to use much pressure when walking but be careful not to pull on your dog's neck. Another option is a harness which works by putting pressure on your dog whenever he pulls.
Whichever you choose, familiarise your dog with it slowly. Put it on a couple of times a day and give tiny treats to associate it with good things happening. After a couple of days you are ready to connect up to your lead.
Exercise is essential to keep our dogs relaxed and happy and of course it has wonderful health benefits for us too. Happy walking!