Based on my expereince here is the list What not do while investing in stocks..

• Do not panic sell
• Do not buy all at once .. i.e. plan DCA
• Do not invest in one sector i.e. diversify
• Do not buy penny stocks
• Do not fall for scams.. telling you that buy this stock it is gonna rise..
• Do not invest if you cannot afford to loose...

Maybe, I will do a post from my side as well and highlight these pointers and much more talking based on my expereince.. Good Luck & Cheers..