Decide how much money you are willing to Gamble in the markets (invest or trade are just softer words that hide the true meaning of what you are really doing. In short everyone is really just simply gambling the stock market is one huge giant casino). 85%-90% of investors lose their money and this must happen for the remaining 10-15% to make a killing. For every dollar won someone has to lose a dollar; hence if you win 5 dollars someone had to lose 5 dollars or 5 people had to each lose a dollar.
Break the money into long term and short term investment portfolios. In each portfolio you should always maintain some cash for those mouth watering opportunities that come along every now and then.
Decide how much you want to make in advance in both portfolios and stick to these figures. Do not keep changing or altering the numbers.
Decide how much you are willing to lose, for example 10,20, 25% etc. I generally suggest for long term plays that you set a mental 25% stop and for short term plays 15% stop
When your stop is hit exit, never widen your stops and as soon as they are hit get out.
If the play is not working out, i.e. not doing anything for months, this is dead money. You have to make a decision to stay in or sell and buy something else. If you have plenty of cash then you can sit it out, but if your funds are limited you might be better of investing in another play.
Make sure the goals you set are realistic.