Your blurry photos aren't your fault, maybe!
Do you have an iPhone 6 Plus? Did you buy it between the September 2014 and January 2015? Then your out-of-focus photos might not be all your fault! Apple announced that there is a defect with the front camera and they will be fixing it free of charge at any authorized retailer.
You can enter your phone's serial number here to check if your phone is from the faulty batch, or if you're just not good at iPhone photography. Fingers crossed that it's Apple's mistake, and not due to your inability to focus long enough to take a picture!