I developed a trivia game a while back for Android that allows you to compete head-to-head against anybody in the world that is available, in real-time. This is in real time because you can see what the other player is selecting. Since I was familiar with PHP and MySQL, that is what I chose to use on the server side to handle everything. I know this can't be very efficient since the game is constantly sending/receiving information to/from the database throughout the whole round as fast as it can. This has been working pretty good for over a year now, but I really haven't had a ton of players on at the same time, and I know there has to be a better, faster, and more reliable way. I'm planning on making this a 4 player game and I know the database will be getting hammered and will be harder to keep all of the players in sync.
What would be an appropriate way to do this? Is this something for sockets? Is the method I'm using now ok for real-time play and I just need to concentrate on improving what I have?
Raw sockets need you to handle a lot of issues. Mobile networks can disconnect easily. What you are looking to develop is similar to a chat application where you send data between users. Php by default is not best suited for this.
You could build this around an XMPP server. The key is being able to send asynchronous responses to the clients. If you need more control, you could build this on frameworks like socket.io or SignalR.