Two trace options exist in BRFplus:
Lean trace and technical trace. The lean trace provides detailed information of all steps of rule processing. It requires versioning to be on and is ideal for scenarios where detailed information is required such as audits.
The technical trace is ideal for debugging rules. The technical trace is used in the rule simulation tool. It is run in interpretation mode where no data is persisted during testing. While some have said real men dont use technical trace :-) I find it ideal to quickly see step by step what objects are used and results are returned at runtime for rules processing. A nice feature coming as of NW 703 is that it will be possible to run the workbench simulation in interpretation and generation mode.
Quite often when building rules I prefer to build a bit, check, activate and simulate if the scenario allows it. This way I am able to quickly check that I am still on track with the end goal of the rules use case.
A feature I have been looking forward to for some time is to be able to export the simulation. As of 702 SP09 this is now available. You can export the rule simulation to an excel document for easier analysis.
Of course there is a lot more in terms of tracing that BRFplus offers, there is the trace API with the ability to call the trace through ABAP code. You also have the possibility to call your rules application from ABAP code and use debug mode to understand what is happening and determine if the correct results are being returned.