"I would not be excited about jumping in here because ... we're not giving up enough," Cramer said on "Squawk on the Street."
The "Mad Money" host said caution is extremely important when geopolitical incidents roil financial markets. While it may be tempting to look at slumping stocks that would be unaffected by further tensions with Iran, Cramer said Friday is not the day to buy them.
"This is Day One . I'm not saying it's the end of the world, I'm saying Day One is rarely the best day," Cramer said. "Day Two you start seeing the opportunity to buy a Pfizer or [Eli Lily]."
Patience from investors is particularly important, Cramer said, because of the strong performance U.S. stocks had last year. The S&P 500 rose more than 28% in 2019 and markets continued to show strength Thursday, the first day of trading in 2020.
With Friday's early declines of about 0.6% to 0.7% across the major indexes, "we're just giving up what we've had for the last couple days," Cramer said on "Squawk Box." "So I'm not telling people to jump on this one."
U.S. forces on Thursday launched an airstrike, ordered by President Donald Trump, that killed Iranian military leader Qasem Soleimani.
The Iranian government said it will retaliate for the death of Soleimani, who was in Baghdad, Iraq, when he was killed. The U.S. State Department has advised American citizens to leave Iraq.
The incident, which caused oil price to surge, escalated the tensions between the U.S. and Iran after a violent few days in the Middle East.
An American civilian contractor was killed in a rocket attack on an Iraqi military base last week, which prompted Trump to order airstrikes Sunday on an Iranian-backed militia group who the U.S. said was responsible.
Those strikes — in Iraq and Syria — killed 25 fighters in the Iran-backed militia, the Kataeb Hezbollah. They caused supporters of the Iraqi Shiite militia to attack the U.S. Embassy in Baghdad, smashing a main door and setting fire to a reception area.
The Pentagon said Soleimani had been actively planning attack on U.S. diplomats and service members in Iraq and elsewhere throughout the region.
If that is true, Cramer said he thought Trump's decision to order the attack on Soleimani was appropriate.
"If he was a bad guy who was going to kill our service people, isn't it better to prevent that?" Cramer said.
Although oil prices rose by up to 4% Friday, Cramer also advised investors to exercise patience when deciding whether to invest in the industry.
It's a good opportunity for oil companies to sell futures, Cramer said, but "I certainly would not be a buyer of this group."
That's because of the lack of sustained moves to the upside in September, when Saudi Arabia shut own half its oil production following an attack on a processing facility.
"Don't buy them today because you may have to sell them tomorrow," he said.
— CNBC's Mike Calia contributed to this report.