How does one determine which stocks will be profitible and which ones will not?

[The]

It depends on
1) Luck
2) Insider news
3) Knowledge of company or stock profiles
4) How much are you investing?
5) How long can you stomach the weather or prolonged drought?

1) Luck
Luck or to put it better way, people's emotion fluctuating towards your favor. The stock you invested might be overhyped or trending for a couple of weeks while people are investing that stock.If you could make a profit during that period, of course you're lucky. But who knows? Everybody's waiting and speculating if the stock price will go up tomorrow. It is basically greed vs reality check.

2) Insider news
You'd never know what's happening inside the company whose share you invested. They might be developing new technology or new products. Or they might be laying off employees. Only inside people know the company best. If they're buying their company stock a lot, there's common perception that there might be major progress in the company or brilliant performance of the company over the years.

3) Knowledge of the company
You can invest in IT, Warehouse, Transportation, Minerals, Mining, Wire, and such. How much of shares are being traded each day and which area of the business the company serves? Basically companies providing or manufacturing products tend to fluctuate price within a range. For eg. Apple, Google, Verizon, Star Bulk Carrier and such. Their prices do fluctuate, mostly depending on products and how good their products are. Some stocks tend to fluctuate widely, relying much on investors emotion. For eg, Zynga and Facebook. They don't manufacture products. They provide entertainment.

4) How much are you investing?
If you're investing a lot, you must carefully choose which stock to hold and their future prospect. You don't invest in just because the company and stocks are popular, but you don't see any prospect in them. That is not to mean you shouldn't be careful when choosing cheap stocks.

5) How long can you stomach the bad weather?
Normally you must be able to withstand the prolonged drought for at least 3 months; the reason being companies announce their quarterly profit and if they don't make the cut, the stock price goes down until they update another quarterly profit. This could go for years until their price come back to where they were before. Everybody's speculating.

Here comes a complicated scenario. Some are said to manipulate their stock prices. They let their stock plummet where they can buy with cheaper prices. Then they announce higher profit returning and stock price goes up and they sell it. Although it is unethical, you never know if there has ever been such a practice. For major investment banks, even a slightest changes in stock price to cents can render a huge profit or loss to them.