You can (and should) enable best practice checks for the MorphX and X++ developer environment, which is similar to the dotNET FxCop code analysis tool. Though the standard Microsoft Dynamics AX 2009 code does not have any best practice errors, you can still find a lot of warning and info type problems.
Update: Microsoft just released a new version of the BP document, which is available here: Microsoft Dynamics AX 2009 Development Best Practices White Paper
To enable best practice checks, go to the menu under Tools/Options, then press the Compiler button on the right. You have to set Diagnostic Level 4 to enable the compiler to check your code for necessary and possible optimizations.