Gta5 do i invest in anything before i start the Merryweather Heist?

Hi people, hoping someone can help me before I start this heist on Gta5. I've invested in other stocks before starting certain missions to get the most money I can however I can't find any info online as to what to invest in before starting this. Is it right there is nothing I should invest in before I start this?
Thanks for the help :-)