If you travel across Russia
This might be helpful
Apps:
Taxi:
ЯндексGo
Uber Russia
City Mobil
Internet, sim card:
Tinkoff (easier but more expensive + might create a bank account)
Beeline
МТС (cyrillic )
Мегафон
Public transport:
buy the card Troika/Тройка
2gis
Яндекс метро
Яндекс карты
РЖД
Food:
Яндекс Еда

I don't think it's common, the level of security in the main cities is really high and in other cities in the centers especially, it's very safe, but the following advice might spare you out of trouble:

never take taxi without app, sometimes there are people who will demand a lot of money;
never drink with anyone whom you don't know
also it's better not to take any food or drinks from a stranger