I'm not a day trader like a lot of people here are. So my rules may be colored by that somewhat.
Find three or more very simple, uncorrelated systems. Test them until you are confident that they will work for you under whatever conditions you are planning to trade them in. (Some of your rules might entail under what market conditions you will trade which systems.) Paper trade them a bit if you want, then start very small. Build up a little each month. Risk the same amount on every trade. Follow all your rules, no matter how you feel about carrying them out at the time. Remember that your trades are not you. Losses are just a cost of doing business. Keep track of every trade. Keep going. Don't quit, don't give up. Go back on the weekend and dissect everything, so you can learn from it and refine your systems and your rule-following behaviors as necessary.
The main thing is just to have precise rules in which you are confident and to follow them, keeping all trades approximately the same size. This is really no harder than making cookies--it is like following a recipe. I have no idea why people find following rules so hard. I am grateful for my rules. (Then again, I notice a lot of people are terrible cooks.)
There are successful traders who use their emotions or intuition to trade sometimes. I personally don't know how to do that. I'm too concrete and I am wrong too often to use a method like that.