I'm a big fan of 'marker training'. And its never to early to start.  You must reach to puppy / dog to follow a treat as a 'LURE'. The 'mark' indicates my approval to my trainee labrador. Where my wife uses a 'clicker', to mark the obedience, I simply LURE the dog with a treat and when they are in position, I say 'yes' as the mark  & give a treat immediately the dog performs the request. The 'mark' is the indicator to the labrador that it has gained my approval and 'the treat is coming'. Don't delay between the mark and the treat. Your dog must associate these two things together. Here's  an example of how you can use a 'mark and treat' while giving a verbal command, "drop": 
Ask your dog to "Drop".
When the dog hits the ground, 'mark', then quickly praise and treat. Do this repetitively so that the dog forms the association between mark & treat.  
Your goal is to maintain the anticipation of the treat. This will keep your dog focused. During you training session, treat more often than not. 
Once your dog understands a behaviour and can perform it consistently, in many different locations, with many distractions, your marker signal and treat / reward can reduce in frequency. You won't need to mark/click and treat every time your dog obeys the command. However, it's important to keep your dog in touch with the 'mark'. 
 You can incorporate other rewards like  throwing and fetching a ball or playing tug. These "real life" rewards can be used in place of treats as your dog advanced in your training program. 

Be ready to use high value treats as you add distractions and greater difficulty. When your dog can consistently focus on the task at hand, you can give lower value treats. 
Having determined to use fewer and lower value treats, don't eliminate them altogether. The use of  food treats are essential as rewards, particularly as you advance the level of training. If your dog has 'low food drive', you will have to use 'high value treats' like cheese or chicken. Labradors do not normally have low food drive.