Train your ear and mouth with minimal pairs that differ by vowel length/quality.
Practice pairs that differ in ONE sound. Start slowly, then speed up.
Do not change multiple sounds at once; keep the consonants the same.
Which sound is different? Is it vowel length, vowel quality, or both?
💡 In many accents, /ɪ/ vs /iː/ differs by length and tongue position. Use a mirror: /iː/ is often tenser and slightly more spread. British vs US note: vowel inventories and exact targets differ by variety, so choose a model (UK or US) and compare yourself to that model consistently; the minimal-pair method still works in both.
✓ship /ʃɪp/ vs sheep /ʃiːp/
A small vowel difference changes the entire word.
✓full /fʊl/ vs fool /fuːl/
Length and lip rounding can differ.
✓live /lɪv/ vs leave /liːv/
Vowel length/quality can change meaning and grammar.