I think Sobrique's idea is the place to start. One of the first things you should teach any dog is to look at you on command. Clicker training is a really good technique and their are a lot of sites out there. Karen Pryor is one of the originals to teach it in modern times, but it goes back at least as far as Pavlov. You may have heard of Pavlov's Dogs. He would ring a bell before feeding his dogs and after a time, he would ring the bell and they would start salivating. It's also called operant conditioning and its about linking two things, a signal and a behavior with a bridge. A gesture or word can be the signal, the behavior is whatever you're trying to achieve, be it the whole action or a partial action building to the main action, and the clicking noise of the clicker is the bridge.
Many people use the clicker because it's easier, but others mark with their voice, because it's always with them. You can say, "yes" and achieve the same results as long as you say it the same way every time. The key is to mark the exact behavior, the second it happens. The traditional way to teach the sit is to hold a treat over the dogs head, wait till he starts to sit, say "sit" as he's sitting, and when he does, say "good boy" and treat him. The problem is that animals, not understanding human speech, associate the reward with what they were doing the exact second they were rewarded. Even in this instance, where you're standing right over them, they could be doing any number of things before the treat enters their mouth. They could be starting to get up out of the sit and think you're rewarding that.
So the clicker marks the exact instant they do the action you want and makes it much easier for them to understand. Think if you're in a foreign country and don't speak the language. If someone asked you to sit in a chair, which seems stupidly simple to them, you wouldn't understand. If they sit you in the chair and make positive noises, you'll understand what they were asking even if you don't understand the praise, and you'll know what cues to look out for next time.
The first exercise usually taught with the clicker is called "charging the clicker". You click and hand your dog the treat. You repeat this over and over until the dog understands that the click equals getting a treat. This is often observed when they start looking at or pawing the clicking hand instead of the one that holds the treat. You can get them looking at you instead of the clicker by simply waiting. They'll eventually get frustrated that the treats aren't coming and glance at your face. Click and treat. They may think it's a fluke, but with repetition, they'll understand looking at your face gets the click and hence forth the treat. They'll start staring at you. You don't have to wait for them to look away. If they keep looking at you, click and treat again.
When any behavior is down solidly, you can begin adding a verbal cue as the behavior is performed. Like saying, "sit" as you click. Then back it off, so you're saying it slightly before they sit. If they ever get confused, back off and work on the basics. Take baby steps. A 1% gain every day is a 100% gain in 100 days. Also, always start with no distractions and work them in gradually. You can't teach him to focus on you for one day and expect him to do it when you take him outside where there are squirrels. You also can't expect him to want a piece of kibble over a squirrel, so offer hot dogs in those situations. The reward you have has to be better than the one he thinks he's going to get.
Use these same methods to teach him to yield to the leash. Put slight pressure on the leash asking him to move in any direction. When he moves to create slack in that pressure, even a half step, click and treat. repeat till he moves away from the pressure, then when you walk him and he moves ahead, just apply pressure till he falls back where he's supposed to be. Good luck.