English puts the present after when, even when it's talking about the future: When you come to Paris, I'll show you the city.

French is more logical about it: if the action is still to come, both verbs go in the future.

• Quand tu viendras à Paris, je te montrerai la ville. — When you come to Paris, I'll show you the city.
• Quand je serai fatiguée, je rentrerai. — When I'm tired, I'll go home.

The same goes for lorsque (when, a little more formal) and dès que (as soon as): Dès que j'arriverai, je t'appellerai. — As soon as I arrive, I'll call you.

But a general truth or habit stays in the present: Quand il fait beau, je marche. — When(ever) the weather's nice, I walk.

Venir has the future stem viendr-: je viendrai, tu viendras, nous viendrons.