Your daytrading system should allow you to start small and grow big. A good trading system allows you to start with one or two contracts, and then increases your position as your trading account grows. This is in contrast to many "martingale" trading systems that require increasing position sizes when you are in a losing streak.
You probably heard about this strategy: Double your contracts every time you lose, and one winner will win back all the money you previously lost. It's not unusual to have 4-5 losing trades in a row, and this would already require to trade 16 contracts after just 4 losses! Trading the e-mini S&P you would then need an account size of at least $63,200, just to meet the margin requirement. That's why martingale systems don't work.
Principle #7: Automate your trading.
Emotions and human errors are the most common mistakes that traders make. By all means you have to avoid these mistakes. Especially during fast markets, it is crucial that you determine the entry and exit points fast and accurately; otherwise, you might miss a trade or find yourself in a losing position. Therefore you should automate your trading and look for a trading system that either already is or can be automated. Automating your trading makes it free of human emotion. The buy and sell operations are all automatic, hands-free, with no manual interventions and you can be sure that you make profits when you should according to your plan.