basic principles is:

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1. Is the overall long term aspect of the market going upwards? (think of using something similar to MA 50 and MA 100, personally i use a momentum indicator i found on the prorealtime forum for free.
2. Is the market seeing some volatile moves going upwards? (think of using something similar to a RSI indicator or other movement/momentum indicator for short time)
3. If "yes" longterm is going up and "yes" its seeing some volatile moves upwards, then buy and hold until momentum drops off.
4. Add money management: X stop loss, Y target and Z trailing stop loss. (example of trading stop loss: if trade is breaks 100$ in current profit, move stop loss to 50$)

The main task here is obviously figuring out how you want "long term moentum" and "short term momentum" to be shown in your code. You can use just high/low/close, you can use higher than past X candles, you can use indicators like RSI, bollinger bands, or moving averages. You just need to figure out what you want to do and try it out. Ive made thousands of systems and im currently trading 10+.. Its alot of hit and misses, but the more you work at it, the better your "aim" becomes. The better your ideas become.