Some rules of thumb can be applied which all basically mean the same thing - trade with the trend. The trend is not just what you see on the one chart for your chosen instrument. So, the FTSE will follow the Dow, the CAC follows the FTSE, the Dow follows the Dow Transportation, the Dow and the S&P follow the Nasdaq 100, the FTSE follows the banks, the Dow follows the $, miners follow gold, airlines follow oil - and so on for ever. These things tend to have some correlations to each other so if you can see signs of an imminent collapse in the Dow/S&P, the FTSE will probably follow and even if the company you are thinking of buying in the UK market is unknown in the US, its price will be very unlikely to go the opposite way to the rest of the market for long.
Of course, its not always wrong to buy the only rising bank in the FTSE banking sector, but you need a damn good reason to do so and need to acknowledge that the risk is that much higher if you do. And proving you are right and the market is wrong should just never be an objective for traders who are uin it for the long run.