A good place to start is by not selling lower than you bought them.
Some people on here don't seem to get that one right.
do you mean that if I bought BTC at 30$ I must keep and wait until the price raise again above 30$ ?
This may be or may be not a good strategy...
In general, trading strategies that prescribes rules of action based on the price you paid are wrong.
The price you paid is the past and you cannot change it. Trading is a bet on the future.
The only things that counts is your prediction about future prices.
The general strategy for trading is this: start with half of your capital in BTCs and half in dollars.
When you feel like it's time to bet on the increase in price of BTC, move some of the capital from dollars to BTCs, viceversa if you want to bet on the decrease of price.
The amount of capital that you move must be proportional to the estimated probabiliy of increase or decrease of the price.
If you you can't tell what the future will be, keep your capital split equally between BTCs and dollars, that is equivalent to not betting.
How you can predict that future price and the probability of it, is another story....
Yes, that is exactly what I mean. I am pretty sure that at *some* point in time, the exchange rate will come above $30 - so it would in my opinion be dumb to sell under that price if you paid $30 for your BTC and want to speculate with it.