The best thing you can do is keep it simple the simpler the better but anything less than simple is just being simple.
hope that riddle makes sense keep practicing on your
demo account.
the word system can mean anything does to different people collectively it is just the process which formulates your trade decisions (buy/sell) governs your trade outputs (profit/loss). dont think of it as being rigid unless you are wanting to develop something automated mechanical it doesnt have to be rigid if you dont want it to.
in due time you will discover what type of trader you are may even find yourself having to develop something rigid to maintain your discipline. just remain flexible open to new ideas at this point untill you discover what works doesnt for you.
then just be rigid on the things that do work flexible on the things that dont actually drop them like a lead weight.
regards