The key to winning a Risk game easily is looking small but painful.
•Don't take Contients fast/Take countries one at a time
•Don't pick on people harshly/Pop them but only on one border, or just weaken them down, only do this if they are big.
•Make treaties/Those who have more treaties are more likely to win than others because they have less number of players to fight with.
P.S. Thank you Dan12