I guess it depends if you’re holding for minutes/hours intraday, days in a swing, or months, years, decades long term.
Depending on the stock I tend to look first at what has happened and look at a target I think it will drop to. I try to avoid chucking in too much at once, as you’ll never get that bottom, then keep adding. Once I feel its leaving it I might add a final amount.
Key thing is always have funds, if you are down to 0 you’ll be twiddling your thumbs going ah no it’s dropping I could have bought in here, which I feel is slightly better than going ah I wish I had put more in if it was actually the bottom.
I do like to trade in the first couple hours US, tend to check the premarket just to see what’s happening.
General rules, first hour and last hour are the most hectic. Friday better for selling, Monday better for buying. September is always crap.