"How much and how often should I take it?"
Cannabis is a very safe herb that is effective for many conditions, including essential tremor. In my opinion the best place to start is a sublingual tincture of whole plant full-spectrum extract. This means that the extract contains many of the cannabinoids, terpenes and other compounds found in the plant (THC, CBD, CBN, CBG, myrcene, limonene, etc.). All of these components work together to provide a synergistic effect, which is more beneficial than any of the molecules in isolation. The sublingual tincture takes effect within minutes and lasts for several hours. You may also benefit from vaporizing, which will is faster onset and shorter duration, giving the ability to fine tune the dose. You might want to experiment with different amounts of CBD, THC and different amounts of decarboxylation. Start with small doses and increase as needed. Cannabis is very safe and unlikely to interact with other medications or foods, and very high doses can safely be utilized.