Please check answers to the following related discussion: https://www.researchgate.net/post/Are_there_any_new_ideas_to_get_graphene_from_graphite_by_fast_and_fully_scalable_methods

Direct exfoliation in ionic liquids, though yield is low.

But tailored ILs are reported to give higher yields and ~65% monolayer graphene.. see this doi:10.1038/nchem.2315

By Mechanical exfoliation. It is the simplest method and you can get the best properties. Check also this article of Nature magazine: "Large-scale pattern growth of graphene films for stretchable transparent electrodes"  (Kim 2009)

http://www.nature.com/nature/journal/v457/n7230/full/nature07719.html

You can sonicate (500 W) it in a NMP dispersion. 

If you want to get graphene sheets, you can follow Mauro's suggestion.

If you want to get graphene oxide sheets, you can oxidize graphite flakes first and sonicate the oxidized graphite in water, which will give you graphene oxide suspension.

I agree with Mauro and Joonsuk, further reduction of GO can be useful in getting graphene. What about grinding graphite?

Dear researchers

Thank you for all the help you have given me.

Best regards