The most important thing is collecting the most representative samples for the feature you are trying to date. You should consider origin, transportation, deposition and erosion/burial history of the sample. All of these factors will affect the age your sample yields. Detailed geomorphic documentation of the sample and its surrounding always helps.
I'm not sure that using cosmogenic dating will help you very much with Pliocene or older deposits in Europe. Snow cover is a large uncertainity, as is any calculation of long-term production rates. When I have been out with cosmogenic people they look for the biggest boulders they can and go right to the top of them to sample.
John Stone, Robert Ackert, and Mark Kurz may have more answers for you in their papers. Consider looking at the CRONUS site at this URL (although it needs an updated publication page) or this URL for the Purdue PRIME lab (extensive publication list).