Sorry, are you being serious?
I naively supposed that someone claiming to have a C1 level in English should know what IPA, transcription and dictionaries are.
Moreover, the examples you are referring to don't have long or short sounds. They have different sounds which have to be pronounced differently technically.
"but" has /ʌ/ in a strong form /bʌt/ and /ə/ (schwa) in a weak form /bət/
"butchery" has /ʊ/ /ˈbʊtʃəri/
"angel" has a diphthong /eɪ/ in a stressed syllable and /ə/ (schwa) in an unstressed syllable /ˈeɪndʒəl/
"and" has /æ/ in a strong form /ænd/ and /ə/ (schwa) in a weak form /ənd/
I learned by learning the IPA pronunciation system. It teaches you how to place your tongue to make the required sounds. Then I'd look for the IPA pronunciation of words I didn't know how to pronounce. Another thing that help was the book Ship or Sheep by by Ann Baker, which teaches pronunciation by comparing pairs of sounds that sound similar. For instance, B vx V, G vs K.
I still have the accent but those two tips helped me improve my pronunciation.