A couple of different ways. The most efficient is to get your assist links all to level 9 on your position 1 (gives just over 500 int) and then going for cave keys in the moon coin shop to get 1050 every cave key rebate to stack your position one (and then use ultimate essences on your position 1 tool).

By far the highest int gain is by leveling up your refines but that also takes the longest.