Step 1: Disclaimer
Caffeine is a deadly poison, do not exceed a safe dose unless you are prepared to experience shaking, feeling like you are going to die, and/or actually dying. When handling it take appropriate safety precautions and wash your hands afterwards. DO NOT LICK YOUR FINGERS AFTER HANDLING CAFFEINE.
If under 18 undertake this experiment only under the supervision of an intelligent, competent adult.
I ACCEPT NO LIABILITY FOR ANY ACCIDENTS THAT ARISE AS A RESULT OF PERFORMING THIS PROCEDURE.
That said, if you follow the instructions carefully and apply common sense this is a fun, safe and rewarding experiment.
Step 2: 'Ingredients'
A high precision scale (one that reads to .01 of a gram)
Citric acid (or another food grade acid)
A disposable pipette (not strictly needed)
All of these are just a google search away.