General:
* Qu'est-ce que tu essaies de...? (Most common) - This is the literal translation and works in most cases.
* Que cherches-tu à...? - This means "What are you looking to...?" and can be used when the action is more about seeking something.
More specific:
* Qu'est-ce que tu essayes de faire ? - "What are you trying to do?"
* Qu'est-ce que tu essayes de dire ? - "What are you trying to say?"
* Qu'est-ce que tu essayes de me faire croire ? - "What are you trying to make me believe?"
Example:
* Qu'est-ce que tu essaies de me faire croire ? - This translates to "What are you trying to make me believe?".
The best translation will depend on the specific situation and what you want to convey.