Finding other board game designers
Designing alone is the slowest way to design. Other designers spot problems you cannot see, trade playtests with you, and keep you moving when motivation dips. Most cities have more designers than you think, and online communities have made distance almost irrelevant.
Online, the biggest hubs are Discord servers dedicated to board game design, design-focused subreddits, Facebook groups, and the BoardGameGeek design forums. All of them welcome beginners. Lurk for a week to learn the tone, then start posting: share your one-pager, offer feedback on someone else's rules, and join scheduled online playtest events.
In person, look for Protospiel events (weekend conventions devoted to playtesting unpublished games), design nights at local game stores, and playtest areas at larger conventions. One weekend at a Protospiel typically advances a design more than months of solo work, because you can test, revise, and retest with experienced players in a single day.
Give more than you take. The designers who get the most feedback are the ones who reliably show up to test other people's games. Reciprocity is the currency of every design community.
Video tutorials
Graphic Design for Board Game Designers!
A Carcassonne Parable for Game Designers: Gathering Playtester Feedback