When. At the start of the working day, or before any undertaking whose outcome is not in your hands — opening a shop, beginning a shift, sending the application.
The words. As'aluka min fadlik — "I ask You of Your bounty". The preposition min is doing quiet work: it means "from", a portion of, not the whole. Nobody asks for all of it. Asking for a share is the form the request takes, and the share is left unspecified.
Fadl is not payment for anything. Its root means excess, what is beyond the necessary — the surplus given for no reason owed. It is deliberately paired with rahmah, mercy: bounty is what you receive, mercy is why. Then the closing clause, la yamlikuha illa ant, gives the reason for asking here rather than anywhere else. Yamliku is possession with the power to dispose — an employer may pay you, but he does not own the thing being asked for.
Where work fits. Nothing in the supplication asks to be spared work. It is said at the start of work, not instead of it, and the two coexist without tension: effort is the ordinary route, and the route is not the source.
Why bounty and not success. The request is not for the deal to close or the shift to go well. It asks for the surplus, whatever form it takes — which is a wider request than any specific outcome would be, and cannot be disappointed by a particular day going badly.
In practice. Short enough to say in the doorway of the office, which is where most people say it.