Some tips Е vs Ё:

1) е is similar to 'Yellow'
2) ё is similar to 'York' (r is not pronounced), equal to saying "йо"
3) ё is ALWAYS stressed, е - sometimes stressed, sometimes unstressed
4) ё used to always be present in the past, but in contemporary Russian the letter е is often used instead of the letter ё (but it must be pronounced as if it's ё - that's the real problem and issue, SOUND is not changed, LETTER is changed in writing)
5) if you see ё in writing, most likely it's because the writer wants it to be there for clarity (but the dictionary following the rules of modern writing may use е in that case), or a writer wants foreign students to see the real sound and uses ё (but the dictionary may say е)
6) the general trend in modern Russian is to stop using the letter ё. But there is a persistent trend, as I can see, that insists it's absolutely important to retain ё in the Russian language.