From what I understand, glow plug errors will not enable the DPF to regenerate.
Firstly, get yourself familiar with the hidden menu to check your coolant temperature. Then get yourself a BMW C110 scanner (I bought mine for ÂŁ35 new) and check 'DME control unit' for any errors. Erase the errors if any present but make note of the errors stored incase if something needs attention.
Once you've started your car before your long drive, scan ecu for any faults and erase memory. About 10mins into your journey, your DPF should start the burning(cleaning) process. Ideally, you would need to keep the revs above 2000 rpm and do no more than 70mph. I would advise 60-65mph. If you've got the bmw scanner as mentioned above, it will show a visual indication that the DPF is regenerating. Regen typically lasts for 15-20 mins.
The main requirements are more than 15 litres of fuel, 75+ degrees Celsius of coolant temperature, engine revs above 2000 and no DPF or glow plug errors stored in the ecu, as whilst these being present, will not enable the DPF to regenerate.
Kind regards
PS hope this helps