One rule I always follow is that every single trade has to be the same size. If the trade passes all the tests which confirm I should make the trade, why would I not put in the maximum stake my money management rules allow?
If you find you're unhappy with the size of a trade, the way forward is to work out what factor is a concern, not to just trade smaller.
Alternatively keep a record of your trades and see which you get better results from, especially in forex. Then up the size of those trades and vice versa.
How do you trade differently based on the size of your positions? What systems should be known in order to know what our position is before every order we send?