Score one for the stoners: The pot industry is poised to be gigantic as more states embrace legalization. And, if you want to get in on the ground floor, several advocates say now is the right time to bet big on marijuana. "Overall public opinion of marijuana has changed," said Dan Humiston, president of the International Cannabis Association. "The stance has just softened. With time as the population ages, a lot of the generations that were really opposed to it are being replaced with the generations that are comfortable with it." Bloomberg reports that the cannabis industry had a market capitalization of $3 billion as of April. There's currently more than 50 publicly traded pot-related companies. Twenty-four states have legalized medical marijuana, and recreational use for adults has been approved in Washington, Colorado, Alaska, Oregon and Washington, D.C. Read More Marijuana Country: The Cannabis Boom

With more companies going public every day, the still illegal industry is growing rapidly. New Frontier Financials, a big data shop that focuses on the marijuana industry, estimates that the industry will reach $15.2 billion by 2020. At least seven states are expected to have marijuana legalization initiatives on their 2016 ballots. Humiston believes that as more states come on board, the hysteria that was overvaluing companies has died down, so prices are more realistic. It also helps that the stigma of being in the weed business is quickly fading away thanks to celebrities like Tommy Chong creating their own weed brands and high profile investors like Peter Thiel, said media and public relations expert Cheryl Shuman. In January, the PayPal co-founder's Founders Fund took a minority stake in Seattle's Privateer Holdings. The company runs a medical marijuana growing operation in Canada and a pot review site called Leafly.com, among other marijuana-related businesses. Read More Peter Thiel's fund buys into marijuana business

"Investors want to see if an influencer, a trendsetter, a cutting edge individual gets involved," explained Shuman—who calls herself the Martha Stewart of marijuana. "Now I'm getting 10 calls a week."

It's important to note that the business is still illegal. Ryan Hurley, partner of Rose Law Group in Scottsdale, Arizona, admitted during a panel at the 2015 Cannabis World Congress & Business Exposition in New York on Thursday that when clients ask him to protect them from going to jail, he can't 100 percent guarantee it. While the federal government has recently turned a blind eye to companies who follow state regulations, Hurley said the policies could change after the 2016 election. "This is still federally illegal," he told CNBC. "I get a lot of people who come in and talk to me because I'm a lawyer. Can I set up some corporate structure to protect them? They can still go to jail for doing this. It's the number one thing to keep in mind." If you're willing to take the risk, Hurley pointed out that while Washington and Colorado already have a heavy concentration of businesses, newly legalized states like Alaska and Oregon have more opportunities to get a license for a growing facility. He added Colorado is also notoriously hard for nonresidents to start marijuana-related businesses on its soil. Read More Cannabis delicacies: 8 alternatives to the joint

Hurley said states that will likely pass some sort of legalization next year, such as Arizona and Maryland, might also be a places to start scoping. He said it seems that it will remain difficult to establish a business in areas like New York and Minnesota. If you want to forgo the licensing process and invest in an existing company—which is safer—Hurley said to make sure that the company follows state regulations. States that have legalized for adult use rather than just medical tend to have more existing rules, leaving less ambiguity and less legal risk.

Medical marijuana growing in Denver Harriet Taylor | CNBC