The first time Android needs to open a particular file type, whether an image or PDF, you'll be asked which app you want to use. Having your phone know your preferences is handy, but it can be frustrating if you change your mind down the road. Here's how to get back the freedom of choice.
Setting default apps
Any time Android encounters a file type that isn't associated with one particular app—be it a URL or an MP3—it scours the system for compatible apps and asks you which one to fire up. By selecting Always you can commit to using this app again in the future every time for this particular type of content.
You could select Just once and make a selection each time, but there's no need to put yourself through the inconvenience. If you ever change your mind (there's an amazing new browser app in town, perhaps) then it's not difficult to undo.
Clearing default apps
You'll need to make a note of the app that's currently opening the file type you're interested in. Head to Settings then Apps and find the app in question: from the app's options page, tap Clear defaults and you're good to go.
Unfortunately there's no way to fine-tune this if an app is associated with several file types. So if, say, you open images from three different places in Gallery and want to switch to Photos for one of them, you'll have to re-select a preference for each source. The next time an open command is initiated, the decision screen appears again, complete with all the compatible apps that are currently installed.
Apps vs Web
You probably don't think too much about the battle between native apps and the mobile Web while you're WhatsApping your friends, but many app selection screens give you the choice of opening certain links (Facebook, Twitter, IMDB, YouTube) in the associated app or in your mobile browser.
You'll often get more functionality if you choose the app option—developers are much more keen to get you installing apps than visiting mobile sites, after all. However, if you set a lot of these choices to your browser instead it's a good way of reducing app clutter on your phone or tablet and keeping the likes of Facebook and Twitter away from your device. It's up to you.
Hopefully this helps you clear up any app-chooser's remorse! Any other tips for dealing with default selections? Share them in the discussion below.