I've done a few solo dives now and I have to say I prefer it to diving recreationally with a buddy. There is a local area at a nearby lake where divers train. There are ropes laid out on the bottom which many divers follow to familiarize themselves with the area. I've been practicing my solo diving here as it is extremely familiar and there are literally "paths" to follow. I feel very comfortable diving here solo and as others have stressed, diving solo in a familiar area is a better practice than being a stranger in a strange environment.
I have dove solo both with doubles and with a single AL80. One key component of my dives is to return with a third of my gas. So far, so good and if folks chuckle because I came up with 1000 - 1200 lbs of air well, let 'em laugh. I had more than enough gas in case of a problem.
I should mention that when I have done my solo dives (to date) at this site there are always other divers from my LDS present (usually conducting classes for new students). While I don't dive with them I do inform one or two of the instructors what I plan to do and when I plan to return. I let them know where I stash my keys, which car is mine and where any pertinent paperwork (like my Health Card) might be found in case of an emergency. While it won't help my safety on the dive at least it may raise some red flags if I'm not seen at a time when I should be back.
Finally, I tend to float a lift bag on most of my dives for my safety stop. I have two reels; an OMS reel and a finger reel. I've practiced using both of them with a great deal of success. Best advice I have is to NEVER clip a reel to yourself when deploying lest you take a rocket ride in the event of a jam up. In addition (as previously mentioned) float the marker from 10 feet below your intended stop depth as a safety margin and get yourself slightly negative as you fill and release the bag. Oh, and I prefer the finger reel for the lift bag over the hand-crank reel. It never jams.