In addition to the provisions in the Geneva convention mentioned in Philipp's answer, some nations/militaries have adopted codes of practice relating to the surrender of aircraft. There is, however, no internationally accepted and recognised method of surrendering apart from ejecting oneself from the aircraft.
For example, Australia's Law of Armed Combat Manual published in 2006 states:
8.40 The LOAC forbids the killing or wounding of an enemy who, in good
faith, surrenders or is otherwise hors de combat (out of combat). Surrenders
in air combat are rarely offered. Nevertheless, actions or signals that suggest surrender should be respected. The surrendered aircraft should then be
escorted to a suitable landing place.
8.41 Although relatively rare, surrenders by defecting enemy aircrew of
military aircraft do offer valuable intelligence and psychological opportunities, and should be encouraged.
8.42 Disabled enemy aircraft in air combat are frequently pursued to
destruction because of the difficulty of verifying their true status and inability to enforce surrender. Although disabled, the aircraft may or may not have lost its combat capability. Moreover, it may still represent a valuable military asset. If an aircraft in distress is clearly hors de combat from the information known to the attacking force at the time, then its destruction offers no military advantage, and the attack should be broken off to permit possible evacuation by crew or passengers. If the aircraft is a support or civil aircraft it is particularly important that this rule be observed.
The manual doesn't go into detail about which actions or signals may suggest surrender, but these presumably include lowering landing gear, slowing their speed, flashing their lights etc. However, some nations regard attacks on aircraft to be permissible even in these circumstances - for example the United Kingdom's LOAC Manual has this to say on the topic of surrender by enemy aircraft:
12.64 Although it is forbidden to ‘kill or wound an enemy who, having laid
down his arms, or having no longer means of defence, has surrendered at
discretion’, in air-to-air combat, surrender is usually impracticable and
occurs very infrequently.
12.64.1 In the special circumstances of air-to-air combat the continuation of an attack after an indication by the opponent of a wish to surrender is not inconsistent with the rule in paragraph 12.64, as the enemy pilot who remains in his aircraft cannot be said to have ‘laid down his arms’ or to have ‘no longer a means of defence’. However, if the surrender is offered in good faith and in circumstances that do not prevent enforcement, for example, when the engagement has not taken place over enemy territory, it must be respected and accepted. Surrenders of enemy aircraft and crews should not be discouraged because not only is a psychological advantage gained, but an enemy aircraft and defecting aircrew can provide intelligence which, if promptly and properly evaluated, may be of inestimable benefit to operations planning.