Still waiting to get your invite to Valorant? Here's some official information from Riot regarding how to increase your chances.
Editor's update: As of 5月 2020, beta invites have stopped going out and the beta is ending. The official game launch (free to play) is scheduled for June 2!
Today, Riot further explained exactly how Valorant beta invite drops work in a blog post:
Day 1 of Closed Beta was a learning experience. @RiotSuperCakes and @RiotZiegler are here to update you on yesterday’s launch in EU/NA, clarify some concerns around how you get access, and talk next steps. https://t.co/sb5VtYSEn0— VALORANT (@PlayVALORANT) 四月 8, 2020
Drops are still happening on Twitch over the "next few days and weeks"
Riot hasn't stated exactly how many invites have gone out, or how many will. They are stressing that they want to provide a stable experience, which means they are continuing to limit the amount of invites they send.
Before tuning in to Twitch though, make sure you've followed all the steps to link your Riot and Twitch accounts.
Time spent watching matters
You need to watch at least 2 hours of "drops enabled" tagged Valorant streams to qualify for an invite. Of all the eligible users, a random percentage will be given an invite.
Riot says that you can increase your odds by watching for more than the minimum 2 hours, but states that hours watched also has diminishing returns, so don't feel the need to open 25 streams and leave them running 24 hours a day. Just one is sufficient, when you are able.
Think of watching your 2 hours as dropping a "ticket" into a raffle. Watching "drops enabled" Valorant streams for longer than 2 hours total will slightly increase the size of your ticket, but nothing is going to get you more than that one ticket.
You can get the drop when you're not watching
Once you've passed the 2 hour Valorant watch time, you're eligible for a drop. This means you could tune in for 2 hours and then never again, and still end up with an invite days later!
Don't viewbot on Twitch
While it may be disconcerting to see obvious bot accounts filling the viewer lists, Riot and Twitch are aware of the issue, and have filters in place to make sure that actual people are receiving invites, not bots.
Don't attempt to buy or sell an account
Riot is taking account buyers and sellers seriously, and warns that your account could be banned before launch if you do this.
Sound on or off?
I've heard streamers say that you shouldn't mute their stream if you want the drop. However, Riot or Twitch have not made mention of this, and is likely just streamers wanting people hearing them.
Personally, I got my drop with a Valorant stream muted and minimized in the background.
Good luck getting your Valorant beta invite!