In theory, setting a stop at your entry point will get you out flat, for no loss and no gain. Its a good technique, when your position moves well into profit, to set a stop at the entry so that no matter what, you incur no risk of loss.
How soon do you set a stop? immediately you open a position. This will at first necessarily be at a loss if its hit quickly but it will be a managable loss (see money management). Don't wait to set a stop, set a stop and then wait: after all, what if you go short on Google and then you get hit by a truck? The next day they get a take-over bid and when you finally get out of that coma a week later you could have lost the house.
Also, SB platforms tend to not allow stops very close to the current bid / offer prices. e.g. I am looking at Finspreads price on the FTSE100 March (but same principle applies everywhere). This is available at 5797-5805. But at this moment they will not offer a stop in the range of 5793-5809 inclusive. If I short at 5797, the market would have to fall 8pts before I break even with a manual close, buying at 5797. But it would have to fall by 13pts before they will offer me a buy stop-loss order at 5797 so an immediate stop at the entry point is impracticable. And setting the stop as soon as a fall of 13pts has occurred is likely to lead to it being hit just due to the natural volatility of the index: anything worth trading can move that much in percentage terms in a few minutes.
Like Oscar says, don't trade alone, let us know what you're doing.