Formal:
* Je vais à Londres. (I am going to London.) - This is the most direct and common way to say it.
* Je me rends à Londres. (I am going to London.) - This is a slightly more formal way of saying it.
Informal:
* J'arrive à Londres. (I am arriving in London.) - This implies you are already on your way.
* Je viens à Londres. (I am coming to London.) - This is a more casual way of saying it.
With a specific date/time:
* Je vais à Londres le [date]. (I am going to London on [date].)
* J'arrive à Londres le [date] à [time]. (I arrive in London on [date] at [time].)
With a specific person:
* On va à Londres. (We are going to London.)
* Vous allez à Londres. (You are going to London.) - Formal "you"
* Tu vas à Londres. (You are going to London.) - Informal "you"
Choose the phrase that best fits the situation you are in!