It depends on the metal which is causing your problem. Is it mercury, lead or something else?
The method you use can also depend on your body. Some people react differently to each chelator, sometimes they react for the better and sometimes for the worse.
First, don't chelate if you have silver fillings in your head. You would need to replace them first.
Probably the most clear-cut method with the most support is the Cutler Protocol. This is a method made for mercury, but using DMSA will help with other metals too. If DMSA is too expensive or you react badly to it, there are people who use only ALA for chelating.
Some people prefer IV chelating with EDTA for lead and/or DMPS for mercury.
I've also used the cilantro and chlorella method. It was effective but had more unpleasant side effects than Cutler. Some people think it's dangerous, but I didn't have any serious problems.
There are other methods too which you can find out about by a google search.
Many people will tell you that the key to oral chelating is to take doses every few hours including at least once at night. This is to keep the chelators' effects going. The exact schedule would depend on the chelator, but is typically every 3-4 hours, depending on the method.
Don't chelate without knowing as much as you can about doing it. Chelating is not 100% risk-free, and knowledge will help you prevent problems.