I was a bit worried traveling in Amsterdam alone, but everything worked out great, in part because of the Greenhouse Effect hostel. A few minutes from Centraal Station and from Dam Square, so everything is either a short walk or one tram ride away.
I was in the Red Light room: the room themes are really cool, and add to the atmosphere. Besides being "cool", the room was also very clean, and though it was small, it was big enough for one person to and all her things. It's relatively quiet, but walls are quite thin, so you can hear your neighbors if they are being noisy.
I checked in at 11am or so, and they let me into my room already, and even let me have breakfast that very morning.
Wifi in the bar is good, and I was even able to pick up on it in my room.
Stairs are steep, but that's expected in Amsterdam.
The only tip: If you like having nice shampoo/conditioner, bring your own, since here it's an all-in-one soap/shampoo/etc.