Where necessary, metadata will need recording, perhaps in text files or word documents, and placed in a folder with the data that it documents. This doesn't necessarily need to be structured or in a standard format, although that would be best.
Henneken, E. & Accomazzi, A. (2011) Linking to Data - Effect on Citation Rates in Astronomy http://arxiv.org/abs/1111.3618
Piowar, et al (2007) Sharing Detailed Research Data Is Associated with Increased Citation Rate. PLoS ONE 2(3): e308. http://www.plosone.org/article/info:doi%2F10.1371%2Fjournal.pone.0000308
RCUK - Principles on Data policy http://www.rcuk.ac.uk/research/Pages/DataPolicy.aspx