I found this strategy to be the best and almost certain to get me in a tourney.
After you're done setting you your Location etc., you are in the Tournament screen. Just start spamming the search button over and over again: Click it, let it load the first 5 tournaments, click it again, don't start scrolling up and down, repeat.
What you are looking for, and is bound to appear sooner or later is an Orange tournament (not started yet). Now when you see that one, you will most likely already started clicking the search button again. Don't worry the tournament will be in the exact same spot in the list after one or two refreshes. When you've seen the orange box what you want to do is try to join it as soon as you can. Don't look when it's starting, don't check if its empty or not, just click on it and click join, you are doing this, because it takes literally a second for 50 or however many people to join and fill the tournament.
You might fail the first few times, but sooner or later you'll find yourself in a tournament.