There is a formula for ip, based off of the length of the game and whether you won or lost.
There are only four factors that matter.
1. Custom game, Co-op vs AI, PVP Normal, or PVP Ranked
2. Map--SR, Dominion, TT, etc.
3. Win or lose.
The fastest method is just playing lots of normal pvp matchmade games on summoner's rift. And then, if you've lost all your matches, make sure to get your first win of the day bonus in a quick match against bots before you log out for the day.