There's two main items you can get that's out there.
1. Algae scraper on a stick
2. Algae scraper on a magnet
haha.
Personally, I used the one on the stick just because it was cheap ($2) and because I have small tanks. There's a more coarse side and soft side, depending on how well the algae has grown. You just soak the sponge stick in water and wipe. Repeat. When you're all finished, it looks great. However, my sponge stick is starting to tear...
The other method is more advance. With the magnet (1 attached to front/back) you never have to deal with outside water. This is also convenient because it is precise. You can get them in different shapes, sizes, and colors. I have never used a magnet before, but all goes well.
There's a third way--chemicals. I wouldn't recommend it. Oh yeah, I don't suggest you use a rag.
Hope you found this useful.