Bedrockgames
I post in the voice of Christopher Walken
This very much depends on the edition (especially if you are dealing with 1E or 2E with the classes having different amounts of XP needed for gaining levels). But as a general rule, the wizard should bide his time and wait until he has third level spells before considering an attack on the fighter in the party, while the fighter should strike early, before the wizard gains enough power to turn evil and betray the party. Of course, the wizard, knowing this is the case, ought to feign weakness, and pretend he can only can use magic missile for years that he may surprise the fighter and the rest of the party with chain lightning. And obviously, the fighter, knowing that the wizard knows this, and will naturally use such a deception, should kill every low wizard he encounters, so that he never falls victim to a chain lightning attack. Which means every wizard should live a life of seclusion, until they are level 18: vowing revenge on all the fighters who slayed their arcane brethren.