Many here swear by Andrew Cutler and his protocol.
ALA comes later in the protocol, DMSA comes first. Also, consistency in dosing is more important that high dosing once or twice. I started here: http://onibasu.com/wiki/Cutler_protocol
It basically talks about chelating with DMSA first, or DMPS, depending on response at regular intervals. ALA comes into the picture later. Breaks in between chelation are important too.
I can't really give out any sure-fire advice cause everyone's different and I've never done the protocol.