Attention is the number one exercise you want to start with your dog anytime you are starting your training sessions. You have to capture your dog's attention, add a cue to it, strengthen that cue/behavior by adding distance, duration, and distractions to it.
Your dog's attention should be the first thing on your mind when you start a dog training session in a new area or even in your living room. Set a timer for 3 minutes and get your dog in tuned with you from the go by giving 5 pieces of treats separately and consecutively right before you start the timer. Once you have delivered all the treats hit the timer and start by having your hands behind your back. Of course, it will be quite hard to even capture 1 or 2 consecutive glances if your dog has pent up energy and you didn't do vigorous exercising before this dog training session. I recommend properly preparing to train, by getting your dog to run without stopping and you can do that with a flirt pole. We offer flirt poles for $25.00. If you go in the morning, take your dog's main meal, maybe add a few extra meat treats in it just to add a little extra value when you are out competing with the environment(cut up chicken, steak, use small pea sized pieces) I start out clicking and treating about 5 or 6 times in rapid succession then going right in with the cues I am working on that day, the first one is always attention though. After you proof your dog's attention in front of you, you need to move it to your sides, add it to your other cues and take it on the road.
If you do not have your dog's attention you do not have your dog. Do not move on to harder cues if your attention is not in progress and advancing weekly. If your dog is reactive to other dogs, then build up that dog's attention in home with no distraction then add low amounts of distraction a little at a time until you can have him within 50 feet of a dog park paying attention to you the whole time. This will help this dog make a positive association with those dogs. It will also allow you to get a little closer as long as the dog is comfortable. Attention is my go-to cue when dog's are passing by my Charley. Now, when she sees another dog in our neighborhood she looks at me instead. I can have her in the middle of five or six dogs as long as they don't lick her in the face or charge at her, she will keep her attention on me the whole time when cued.
All in all, giving attention is the single most important behavior to train with your dog. Take it all the way to the point of maintenance. You should be able to say your attention cue and Name and the dog responds the first time, with zero latency, even if he is in front of a small friendly kid holding an ice cream cone dripping down to the ground. You should train attention so much that just looking you in the eyes is a reinforcer to the dog.