I'm working as a vendor to a technology startup but am still unfamiliar with the nuances of stock options. Basically, I have been granted an option to purchase X shares in the company, that vest pro rata over Y years so long as I work with them. The exercise price is "fair market value" as determined by the company's board when I exercise the option. When should I exercise my options? The company is still in its early stages and has not received significant venture funding just yet. Do I just purchase shares as soon as they vest, hoping to capitalize on a high valuation from VCs when it occurs (if not an even higher purchase)?