Knowledgeable investors can determine when it is time to get in and out of certain sectors. Once investors figure out which sectors are the strongest; they can then determine which companies within those sectors look the most profitable.

Bull, Bear, or Sideways Market :

So what is a Bull, Bear, or Sideways Market?Bull markets occur when the major indexes, the DOW, NASDAQ, and S&P 500, are all going up. (GOOD FOR MOST INVESTORS) Economy as a whole is in good shape and investors are willing to put money into the market.
Bear markets occur when the major indexes, the DOW, NASDAQ, and S&P 500, are all declining. (BAD FOR MOST INVESTORS) Investors are basically selling their shares for whatever they can get for them and the economy as a whole is not doing well.
Sideways markets are basically a point when the indexes simply stall out and they are neither going up or down.
Different variations of these trends have occurred at different points in the history of the stock market. The trends can be long or short depending on a wide variety of factors.

Sectors of the stock market :

As you watch CNBC you will hear the term sector being thrown around a lot. A stock sector is a group of companies that belong to a similar industry.
Some examples would be the retail sector, pharmaceutical sector, automobile sector, or oil sector.
No matter how well the stock market is performing overall; there will always be sectors of the stock market that are doing good or bad at different times for various reasons.