It's fairly simple to do... stolen from a first year chemistry lab manual (although this is my abridged version!):
Mix 10g coffee with 200mL distilled water, then slowly add 75mL 5M NaOH. Swirl until dissolved. Place mix in sep funnel and extract twice with 50mL DCM. Empty out the aqueous layer, then pour in the DCM and wash with 50mL distilled water. Dry the DCM with MgSO4. Then distil off the DCM - the majority of the stuff in the flask is caffeine.
You may want to wash the crystals with something, as they can be kinda yuck looking... I'm not sure of an appropriate solvent. And, of course, washing should remove any residual DCM, which may be slightly more healthy if one intended to consume the caffeine...