If you have an iPhone 6 Plus and your photos are reliably trash, it might not be because you suck at taking them. Apple has stepped up and admitted that 6 Pluses sold between September 2014 and January 2015 have a "defective component" on the camera which causes "fuzzy pictures."
Rest assured, though, it's only on the back iSight camera, which, who even takes pictures that way anymore? Selfies all day, bruh. Still, if you so choose you can get the issue fixed and the camera swapped out for free at any Apple store. You can check if your phone is part of the faulty bunch by entering your serial number on this website (serial numbers can be found in Settings > General > About). If your phone isn't eligible but still faulty, may I suggest tapping the yellow square on the camera screen for focus?