There are few things you have to take note of, when you’re creating a system to trade with.

Market Selection:

First you must choose the market you want to trade, the specific instruments you want to trade. That is the first place to start.

Market Direction:

Will you be trading along with the market direction, or against it, or will your system be agnostic to market direction?

Setup:

What are the pre-requisites, conditions as such for you to enter a trade in this particular instrument/product?

Under what conditions will you exit?

These are the entry & exit conditions.

Market Timing / Entry:

Once your entry conditions are satisfied, when exactly will you enter/exit?

What timeframe do you enter/exit in?

Protective Stop

How will you know when to get out? What conditions will you use to stop a trade that’s currently in loss from bleeding more money from your account?

Re-Entry

Often, when you’re using a fixed stop or even a trailing stop most probably, you get stopped out in the middle of a really good trend.

How will you re-enter? What are the re-entry conditions?

Taking Profits

Under what conditions will you take profits? Will you use a fixed profit target, or will you trail your profits?

If you trail your profits, at what point do you exit? Will you re-enter again (6th point)?

Money Management

You should know how much $ you’ll lose when you’re wrong.

Knowing that, you should also know how much you should stake on each trade.

How big of a position will you take based on the information?

Portfolio selection

Given that this system is in place, what all instruments/products can/will you trade as part of this system?

Will you be trading only one instrument or a basket of instruments?

What will be the basis for selecting those instruments?

Multiple Systems

Trading only one system will work in certain phases, and will be in drawdowns in other phases.

Do you want to trade multiple systems to smooth your performance? Will you trade/use uncorrelated systems? How will you choose which systems to trade?