Rewards work best when they clearly mark the choice you want your dog to repeat. That means rewarding the moment your dog does the behavior, not several seconds later.
Keep treats small and easy to deliver. For everyday training, praise, toys, sniffing, and moving forward can also be useful rewards when they match what your dog wants in that moment.
If the behavior is not improving, adjust the setup. Make the task easier, reduce distractions, and reward sooner.