First of all, if you have a family history of mental disorders, like schizophrenia or bipolar, I would highly recommend
not trying any psychedelic. There exists a possibility of uncovering a latent genetic mental disorder that otherwise would not have appeared.
That said, I wholeheartedly recommend starting with Marijuana. It's not a psychedelic in the traditional sense, but it's a good introduction to mind-altering drugs.
From there, either LSD or Mushrooms. These are more typical psychedelic experiences, with long durations. LSD can last 8-12 hours depending on the dose, mushrooms is 6-10, depending on dose and species. I personally prefer LSD, but you should be cautious and ensure you get legitimate stuff. Taking precautions and purchasing off the internet from a reputable vendor is the safest method in my opinion.
When it comes to LSD, I always recommend swallowing over just leaving it on your tongue, especially if purchased from an irreputable source. The common Research Chemicals sold as LSD are only activated sublingually (through the mouth/gums), whereas LSD is sublingual and oral. For a newbie 100ug I believe is considered a light dose, although you could go down to 50ug and still feel Something.
General trip advise would be to ensure you're in a positive mindset, and in a secure, safe, comfortable setting. Taking a walk through nature is nice, as well. Set and setting is important.
I would advise against trying any research chemicals (25X or 2C-X, where X=[A-Z]), just because they are newer and less known, but with the right research and precautions you could be okay.
Avoid mixing until you know what you're doing. A lot of people like to mix marijuana and lsd/shrooms, and I find it definitely intensifies the experience, while clouding it a little.
Overall, you should conduct a lot of research and read people's trip reports so you know what you're getting into. Tripsit.me is a wonderful resource, and includes an IRC channel for support and conversation while tripping. Erowid is a popular site for information as well.