Speech ability, first of all, you should be able to speak. Thinking ability, Russian grammar is very complicated, just like mathematics, it needs thinking and reasoning, not simple rote memorization, so it needs thinking ability.
The second is super patience and persistent determination. Rome was not built in a day. It takes a long time to learn from ignorance to normal communication.
Finally, there is a physiological condition, that is, you should be able to shake your tongue. Russian has vibrato and the best pronunciation, but it's not bad not to pronounce "le".