Convention Etiquette
The core rule of convention cosplay interaction: ask before photographing. This is not universal — large group shots and candid crowd photography are generally expected — but approaching an individual cosplayer and asking to photograph their costume is the correct behaviour and is universally appreciated. Complementing someone's work specifically (not generically) is equally valued: 'the wing construction on your costume is incredible' lands better than 'great costume.'
Online Communities
Reddit's r/cosplay and r/cosplayprops are the largest general communities; specific fandoms have their own subreddits with cosplay sections. Discord servers organised around specific fandoms or construction techniques are excellent for getting specific feedback on specific problems. Instagram's cosplay community is large and visually oriented — hashtags connect you to creators in your specific area of interest.
Giving and Receiving Critique
The cosplay community has developed norms around critique that are worth understanding: unsolicited negative critique is generally not welcome, even when technically accurate. Constructive feedback given when asked for is the appropriate channel. When asking for feedback, be specific about what you want input on — 'does the armour shaping look accurate to the reference?' gets more useful responses than 'what do you think?'
Finding Local Community
Local cosplay groups organise sewing circles, convention meetups, and skill-sharing events. Search Facebook for cosplay groups in your metro area. Convention local forums often list pre-event meetups for specific fandoms. Heidi's monthly sewing circle is an example of this kind of local community — see sewing lessons for details.