I have read many websites, one book, and something that I have seen very common in almost all strategies, sites, videos, its to use the market indices to decide if we should look for long or short postions

So, as I didnt understand a lot about market indices, I went ahead and read little bit about indices.  There are many of them:

This guy here choosed the SP500 to know if the market is down or up, and then decide what kind of positions to trade.

http://www.swing-trade-stocks.com/market-timing.html

Cameron Foous, uses the Down Jones, which is of only 30 companies:

http://en.wikipedia.org/wiki/Dow_Jones_Industrial_Average

So to try to understand more, I ask you guys, do you even check the market indices before your trading day, and depending on that you trade long or short positions?   If so, what indices you use and why? I dont know which ones to choose,  I am a beginner, but how an index of only 30 companies can tell you where the entire market is going?

Shouldnt I use indices with more companies, that represent better the market? like russell 3000 or something?

thanks

yes, as part of a structured approach an overall market analysis analysis is essential, and should be taken into consideration when trading individual stocks.

supposedly 80% of stocks follow the direction of the major indicies.

myself, i'd just soon simply things and trade the QQQ's.

.............simplify things and trade the major indicies, like qqq. spy, iwm.  i also trade gld (gold), and tlt.

if I check the major indices to know the market direction, does it mean that if I do a scan for possible trades I should scan only stocks on that index?

the diection the major averages are trending will affect all stocks.  

you may want to do an analysis of the sector or group the individual stock belongs to as well.