Formal:
* Modlić się (most common and general) - This literally means "to pray" and is used in most contexts.
* Prosić o łaskę - This literally means "to ask for grace" and is used in a more religious context.
Informal:
* Modlić się (same as the formal version, but used in a less formal context)
* Prosić - This literally means "to ask" and can be used in a more general sense, like "I pray you will come."
The best translation will depend on the specific situation and the tone you want to convey.