Mabrur, when I asked different quarters, has slightly different meanings. Some say that it is a Haj that is accepted (by Allah, surely). "Haji yang sempurna" was what others said. Ultimately, they lead to the same, if we analyse what goes into it. It has to be a 'complete' Haj: all checked. Our hearts, our actions, our intentions; all play a part into achieving Mabrur. It is not just about completing the the stoning of the jamarat, for instance, but in choosing the stones (I saw some fellow-pilgrims washing them, even), the time we go there (after fajr), the way we go (calmly and humbly), the way we throw the stones (again, calmly, patiently). It is doing one's utmost best. That's what I believe it to be. The rest should be left to Allah.
The word 'mabrur' itself is derived from 'bir', meaning 'good' in Arabic. This is according to the mutawwif (guide) we met in Makkah. Therefore, again, everything we do must be done as best we can.
In all the Haj rituals, both parts of our relationships must be looked into: our relationship with fellow humans, as well as that with Allah (habluminAllah and habluminannas). That is why pilgrims are asked to seek for forgiveness from friends and relatives and co-workers before embarking on the journey. Thus, the preparation for a Haji Mabrur starts way before the flight to Saudi. Oh, AHS and I had our share of 'tests' way before the actual journey started. I just hope we have become better persons, after all that.