When I teach phonetic transcription, I tell my students that all syllables must have one vowel and only one vowel. (I include a schwa in the second syllable of words like 'bottle' and 'fashion', as syllabic /l/ and /n/ tend not to be used in places like Brunei.),
So I tell them to count the number of syllables in a word and then make sure that they have that number of vowels.
Yesterday, one of the words I gave them to transcribe was 'beautiful', so I asked them how many syllables it has. And they all answered: four. Hmm, no wonder they tend to transcribe it as /bɪuːtɪfʊl/.