The bad news is that Blizzard isn't offering a direct way that you can guarantee access to WoW Classic early.
Following a public demo at Blizzcon 2018, Blizzard has now finally announced the launch date for Classic servers: they will be going live on August 26 for North America and the United Kingdom, and August 27 for the rest of the world. From May 15, Blizzard will be inviting select players into a closed beta, while more will be brought in for stress tests from May through July. Relive classic moments such as when Onyxia "spread terror from her lair", in Duskwallow Marsh, when Leeroy Jenkins did his thing, and more. After fans complained, Blizzard began (not-so subtly) working on a solution to make everyone happy: enter Classic World of Warcraft.
Giving players the chance to return to the game as it was around the time of its launch, WoW Classic is set to launch worldwide on August 27.
Beginning on May 15, certain WoW players will be invited to "participate in a small-scale, focused closed beta test, helping ensure WoW Classic nails its goal of authenticity". For a chance at getting in, you'll either need an active subscription to World of Warcraft, or proof of dedicated playtime on your Battle.net account.
The first stress test will run from Wednesday, May 22 to Thursday, May 23. You can opt in through the official site. Following the release of the game, Blizzard will add in original WoW content in the order of their initial release date.
While the server will not be live until the end of August, players will be able to create their characters ahead of time on Tuesday, Aug. 13.
After much waiting, Blizzard has finally announced its full scheduling plans for World of Warcraft Classic, the legacy server for its 15-year-old fantasy MMO, which time travels all the way back to version 1.12 of the game from 2004.