Early 40s and have a strong 401K but have a desire to invest on my own as well. Where do I begin?

I have a very nice side business that generates about 10k per month, so I'm looking to do some smart investing. I have around half a million in 401k currently, which seems to be about average for my age. My 401k is in Fidelity. Should I just use Fidelity to call my own shots for individual stocks outside my 401k? What do you recommend and any tips for someone my age? Is it better to buy groups of stocks or target single companies?

Any tips or best practices on beginning are greatly appreciated.