Adding ID to data block

Hello Everyone:

I had a query related to writing ID numbers onto the data blocks in the Mifare 1K tags. I am pretty new to libnfc, please bear with my limited understanding of NFC.

I would like to store a unique ID onto the datablock of the nfc chip. My question: if a person has an ID 1234567, in what way should i store it so that i can read it and track the related id from my database. Do i store the number in hexadecimal form? Also is there any particular block onto which i should put the NDEF data. Currently i have put it on block 2 as block 0 and 1 are not accessible.

Any help would be appreciated.
Thanks,
Bipin