You might want to start by noting the order in which fresh crops start showing up at your local farmer's market, talking with the vendors about those crops and how they are doing this year, etcetera. Many wild foods in your area are in the same genetic families as the domesticated cultivars.

This gives you an ongoing baseline even when you are not spending time exploring your wilder environs.

Over time you can begin to note that when a certain certain fruit, flower, herb,or vegetable shows up at the farmer's market, it is likely the harvestable wild cousins you found nearby are also nearing their peak.

Edit: Do check out Blast's website. Good stuff, especially excellent multiple pictures of many plants.