Here's a really quick and handy tip to actually add your custom names to the built in dictionary - so follow these steps and you'll be set!
Go to SETTINGS then GENERAL then scroll down to KEYBOARD
at the bottom you will see SHORTCUTS. These are abbreviations that you can type and iOS will put the whole word in for you - it can be quite handy so I sometimes have ST for Satureyes Photography. Every time I type those 2 letters - it writes the whole word/phrase.
However - this is actually also the custom dictionary, so all you need to do is to click ADD NEW SHORTCUT and where is says PHRASE, just type the word you want it to 'learn'. You don't need to add anything to the 'shortcut' box if you don't want to.
That's it. No more stupid autocorrects!