To all the experienced psychedelic users, what quality advice would you give to someone who has never hallucinated before and would like to try taking psychedelics for the first time?

Hallucinations are 3D projections. They may strike you with awe or make you feel really uncomfortable. How you choose to react is completely up to you. It is a reflection of your inner world. Utilize the experience as a tool to learn more about your potential power.