One of the easiest ways you can increase the engagement level of your dog is to keep them guessing! When we become predictable in the way we walk, play and reward things get a little, well...boring. It's not hard to see why so many dogs choose to engage with the environment over their guardian when we continue to offer the same thing day in and day out.
Concepts trainers consider how to live the best, reinforcement rich life with their dogs. This means figuring out what a dog loves and using those things to reinforce great choices each and every day. When you have a variety of ways to reward your dog for the things they do, you can reach into that reward toolbox and choose something different each time you see an opportunity to mark a good choice. For example, when I have my dog off leash near water and take her lead off I may ask for 'middle' and a few nose touches before sending her off to swim. If she disengages from another dog that is barking at her from across the street I might reward her with a game of food catch as we walk on. After a few minutes of walking on a loose lead I might give her the 'go sniff' cue and reward her great leash skills with a chance to pause and sniff around a tree or bush on route before continuing on.
Variety = Engagement. Spend time to build up your own Reward Toolbox, filling it with things that your dog loves. That last part is key...rewards must be what *your dog* loves, not what you love. A shy dog may see a stroke on the side as intrusive and a bit scary, but may love to catch a yummy treat that is tossed in the air. Keep your dog guessing as to what their rewards will be and see a drastic change in their engagement levels with you.