You decide whether you want/need a sober guide if you give it a try. It's great for some people to have a minder, personally I it a bit repressive (even someone else minder). I've had a few chances to try iowaska but there were all these rules involved like having a minder, dressing all in white that just aren't for me, so I've passed. Know thyself! If you go into it knowing you are going to have a cool time and don't need a minder you will probably do great. Nothing is more true than that the attitude you go into this kind of thing with will usually define your experience. Limit the variables before you try the first time. Be with a person you or persons you know and care about who care about you. If you have some heavy karma to work out with one of those people there is a good chance that you will be doing that at some point so if you don't want to deal with it find other people. Nature is great for this kind of thing. The worst random variables are things like police and parents, use nature to separate you from that kind of stuff. Police, parents, heavy trips and most everything else will just pass if you keep your cool, it'll all be over in less than a half day. Hydrate!
I have to disagree here. It's always best to go in with a sitter for your first time. Even if there's a 90% chance everything goes perfectly well, there's always the chance things will get weird. Not to mention, you can't trust your sober mind to know how your mind's going to work on an eighth of mushrooms if you haven't tried them before. It's just a completely different headspace, and it's always safer to tread carefully when you start out.
I think many people would disagree with me but I'm glad I got to explore the experience with out any intermediary trying to keep my chill. I've certainly baby sat people who seemed like they needed a minder but I wonder if they would have had a more open and honest trip without someone trying to keep them grounded.
I don't disagree that solo trips can be very beneficial--my most insightful trips have always been on my own. I just think people shouldn't do it alone their first time.