if investing in individual companies, you need to do your homework. Look at the balance sheet. For instance, if there is a big asset sell off, watch out.
I do the buy and hold method. My ex elder, non practicing over 30 years FIL day trades but it is a HUGE time investment to do so. He has a group of interested friends that formed an investment group that meets each week to discuss the market and the investments. He has done quite well with his trading. ( be careful about the short term trades becaus you can have big tax liabilitiest that might offset your gains) Personally, I don't have the stomach for it. It would twist my nerves to death. My neighbor both long termhold and day trades, and invests in companies she studies. Also her husband and son are in the technology feild so she listens to what they like and buys there. It has been a great method for her.
I am not so savvy but I have friends who are in one field or another and I ask them what they are investing in. Overall speaking I have not lost money in the crash, but I also didn't make much. Some companies were huge successes, some not so much.
I learned something about inesting and the market while in grad school but not enough to feel very confident. I remember bitds and pieces, like in a depressed economy , historically companies like Jack Daniels, or Health and Beauty industries usually do well. But also in the market you can't always just trust "historically" because the economic enviornment can change enough to make that type of investment not so good.
It's basically educated gambling.