1. Start local blockchain

truffle develop

2. Copy Truffle url into Metamask

After typing truffle develop from step 1, you should see something like this inside the Truffle console.

Truffle Develop started at http://127.0.0.1:9545/

Copy the url http://127.0.0.1:9545/ and set up a custom RPC inside Metamask.

3. Import accounts

Copy the private keys from Truffle console and import them into Metamask.

Here is the private keys listed inside my Truffle console. I recommend you import the private keys that you see inside your Truffle console.

Accounts:
(0) 0xf36467c4e023c355026066b8dc51456e7b791d99
(1) 0x6b1a5bb56b9956e2db2b5584846c5641331134d0
(2) 0x6dd58e6bccc8ba9269783d470e3dda3a6e8d8c7f

Private Keys:
(0) 03f7c8a78d147592992a7b835d3e0cc29e992e6924af7a1fcced5b0d25317c86
(1) 4902221c58878e6e8bccf35d68371b28f06d1fc7bb4e49baf919bf696460f92d
(2) af7592d51c7cde468ec5d45ec3ccda0401d150131876c8db3ca36324c009d837