Pokémon Diamond and Pearl/Route 201

'Route 201 is the first place in the game to catch Pokémon, but more will come soon. Connecting Twinleaf Town to Sandgem Town, Route 201 tests the power of new trainers and their Pokémon'

Route 201
As your first outing, you have no Pokémon, meaning if you even attempt to go in the grass, your mom will come and tell you not to go in the grass so go to the left, to come to Verity Lakefront, and continue from there.

On your second visit to this route, go back to Twinleaf, and Rowan and his assistant will be there, apparently very annoyed. The assistant says to come see them at their labratory in Sandgem Town. Talk to your mom to obtain the Running Shoes. Your rival's mother will come and ask you to deliver a parcel to your rival who is already in Sandgem town.

On your third visit, instead of taking the left path, start through the grass, talking to the PokéMart salesman to recieve a free potion. Continue up through the grass, and to the right to reach Sandgem Town.

On your fourth visit this early in the game, go back to Twinleaf, jumping over the ledges to avoid the grass if you would like to, and talk to your mother one last time. Go back to Sandgem to start on your adventure.