Tough question to ask it varies from stock to stock. This is what i do...
Premarket opens watch who is lining up and at what price... if they are paying over the top the stock might struggle to find its feet and goes into a "cool" period for half the day as buyers be wondering if someone is going to "dump" etc..... the stock will most likely not run again until a long long time... ive seen it alot of times and this would catch the inexperienced retailers. There are alot of factors to why a stock cools down from such a high opening........ SYA morning bullish arvo collapsed.... TON pre announcement bullish afterwards collapsed... you get me...
If it however opens red like RAP today because the stock didnt get alot of attention over night i would buy in a small parcel set a stop loss tight to protect myself from a reversal. if the buyers are increasing during the day and people are chomping at the sell side i take another holding this is where my example of "CHP" ( if you read my posts today) i had buy orders ready. Watch the charts are they forming something everyone likes triangles etc this is telling the signs are bullish..... if they are forming any patterns that favors an upwards trend go for it.... thats imo....
Tomorrow i wont be around as i have uni but hopefully i get to uni before 10. I dont have time but later if not tonight i will do a volume study how many people are holding ... i want to find the point where i can exit well before the dump
ALL the best