I had problems getting my material to stick reliably to the printbed. I have tried all sorts of methods, some with more succes, some with less.
I have been printing directly on mirror for a while with my old printer, and that have worked well with PLA but for some reason it don't work quite as well with my new printer, the mendel90. So I tested and tested to make it work, and noticed that the filament had a tendency to curl up and get in contact with the head-block of the j-head. Looking at the j-head tip (China copy, but I think "original" versions too), it was clearly a relatively large surface just out of the nozzle.
So I thought that if I sharpen it, to make the bottom surface outside nozzle smaller, it'd be more likely to connect to the bed, and less to the nozzle. With a small round file, I filed away some of the nozzle, and made it smaller.
And it seems to work. Both PLA and ABS is now a lot easier to get to stick.
Next time, I guess I should turn it on a lathe.