It's kind of hard to explain in words. For example, if I struggle to say the word Electrical, I bring the edges of my mouth way back, like when saying Eeeeeeeee. In the same way, I pre-shape my lips in a circle for vovel O as in Oooooo, before I actually start pronouncing the word Open. You can also do this for words that start with consonants, just target the first upcoming vovel and the block won't be able to take grip, as your whole face is already uttering the sound.