Preprocessing in Data mining?
The preprocessing will depend on what your data is like: textual? numerical? If in whatever analysis you want to do the data is not allowed to have duplicates, you'll have to filter those out. If not, they'll get to stay, etc. 
If you already know exactly what you want to do theoretically and just need to find some software, python pandas is very good. Load the data, clean it, group it, perform elementary analysis.