German spelling can be tricky to get to grips with when you first start learning, but there's a simple trick to remembering whether the word you're writing is 'ei'  (e.g. 'bleiben') or 'ie' (e.g. 'spielen'). If, when the word is said out loud, the vowel sound you can hear is an 'i', as in 'bleiben', then the word is spelled 'ei'. If, when the word is said out loud, the vowel sound you can hear is an 'e', as in 'spielen', then the word is spelled 'ie'. The vowel you can hear when the word is said is the vowel that comes second in the spelling of the word.