Track Everything
The earlier you set up systems for keeping track of information, the faster you'll be able to hit the ground running in a campaign. Set up a spreadsheet or other database to keep track of contact information, notes, and next steps from each meeting you have. This will make it easier to remind yourself of any outstanding follow-up steps you've promised and is a good way to see how your base-building efforts are growing.
You'll also have your ready-made list for outreach, endorsements, fundraising and volunteers come campaign time!