leave is "лиив". Russian "И" and smile live is "лыв". Russian "Ы" and no smile and mouth is more open

Listen to клык here: https://forvo.com/search/клык/ . It sounds very similar to the short "i" sound of "fill" here of Mr. Taxman's example https://forvo.com/word/fill/ .

The first column is pronounced more in the back of the mouth with a more retracting tongue position--it's more analogous to the «Ы» sound, but less severely so since that sound doesn't exist in English. The second column is pronounced more in the front of the mouth with the tongue moving slightly forward--kind of like the sound is just falling out of the mouth. It's more analogous to an unstressed «е» in Russian.

In my opinion Hadar is a brilliant teacher and explains it great! https://youtu.be/Y3OKnbAaWSs

Listen to native speakers and copy them. Find a teacher who can emphasise what you're doing wrong, and correct you in a way that you understand.