When in the future....

Take care when using 'when' clauses with future meaning. They need a verb in the present or present perfect tense, not the future:

When you see John, tell him I am looking for him.
When you reach London, you should book a hotel immediately.
When I receive your letter, I will look into the matter.

Note: present perfect could be used in the second and third sentences with little change of meaning. This is because the two actions are in a sequence (reach London> book hotel; receive letter> look into the matter). In the first sentence, however, the present tense is better because the two actions are simultaneous (see John = tell him).

Other time phrases which work like this are:

as soon as, the moment, whenever

As soon as you hear any news, please ring me.
The moment the rain stops, the tennis will continue.
Whenever there is good weather, the road to the beach gets crowded.

Note: which of these three sentences could take present perfect tense without changing the meaning?

Present tense is used with 'whatever', 'whoever' and 'however' when talking about present or future events:

Whatever you give, every penny counts.
Whoever you talk to around here, people are very friendly.
However you look at it, the summer is always the best time of year.