The most important date to remember is March 22nd. That's a Thursday. So basically, if you are reading next weeks issue of Indie iOS Focus Weekly and haven't registered yet, you are out of luck. Of course, registration doesn't guarantee a spot, but it gives you a chance.
WWDC is expensive. If you don't want to spend that kind of money, but still want to be around for networking, check out AltConf. It's free!
The opportunity to buy tickets to WWDC18 is offered by random selection. Registration is open until Thursday, March 22, 2018 at 10:00 a.m. PDT
Apple opens WWDC 2018 registration: June 4-8 in San Jose by Zac Hall