One tip I picked up from a friend in japan. When you say each one you tongue should tap the roof of your mouth, but not your teeth like a rolling R sound. I hope this helps :)

Hello Антон, Japanese people are used to hear ら り る れ ろ with an English accent, but not so much Russian. Russians have this 'R' known as the alveolar trill. More commonly known as 'rolling r'. In Japan they do not differentiate between the 'r' and 'l', it's more like a combination of both. And it's quite normal to have difficulty with the correct pronunciation! Don't worry about it too much. The only tip I can give; try to pronounce the 'r' with less power.