Everyone is different, so there is no perfect formula for a good experience.
This is what I suggest, or at least what works for me:
Stay home or go to someone's place that you are very comfortable in. Shrooms amplify every bit of stimuli, so being in an unfamiliar place can quickly turn into a bad time.
Before you drop, clean the place up SPOTLESS. I'm uncomfortable in my own home when it's a mess. If dirty dishes and smelly laundry bring you comfort, then skip this step.
For music, choose whatever relaxes you. If
Deicide brings you peace, then more power to ya. Some of my fav's are
Zero 7,
Air, Starseeds,
Eastern Sun(check out "Rapture at Sea"),
Dzihan & Kamien, any of the
Cafe del Mar albums, and of course, Pink Floyd. Lots of people dig the Goa and PsyTrance music. I've always loved it when on E, but not so much on shrooms.
If there's some wooded areas around you that you're familiar with, a walk in the woods can be straight up magical! The dappled sunlight, the smell, the sounds... Some of my best trips ever were in the woods! Mosquitos on the other hand can make you wish you didn't exist, so proceed with caution.
As far as dosage goes, you would do well to get a scale. In fact, I COMMAND you to get a scale! Digital scales can be had on ebay for $20. You'll pay much more at your local head shop (Purple East?

). Conventional wisdom dictates 1g dry for your first time. Don't do more than 2 until you know what to expect. Psychedelics are not like other drugs in the sense that 4 is not necessarily twice as good as 2. Check out this here . Follow the links and read up on trip level and such.
This is really important... never, NEVER forget that you're under the influence. I've seen people go from slightly weirded out to a full blown panic because they convinced themselves that they were going insane. It's the drug. It only lasts a few hours and then it's over. Don't forget that. Also, never "fight" the experience. Just flow with it at all times.
About your pressure cooker... A gauge is kind of a luxury, but it's not necessary. Lots of inexpensive PCs don't have a gauge. You should find the instructions (usually available online from the manufacturer). They'll tell you how to know when you're at the right pressure. It's usually something like "When the steam escaping causes the weight on the lit to rattle, you're at 15psi, escaping steam, but no rattling weight is 10psi". That's just an example, not actual instructions, but you get the idea

Run it with just water in it first to make sure it works fine.
Let's see, what else... Oh yea, discussions about any aspect of buying or selling illegal substances are frowned upon 'round here. Nobody will probably answer that question anyway, but just so ya know
please do not post links to the shroomery....