Effective trading requires sliders to be optimized for it, towards Plutocracy, and Free Trade. While there are some restrictions for Plutocracy under Feudal government types, you want to get as close to plutocracy as you can to be ready for the point you can change to better government types.
Secondly, in Vanilla, take National Bank early on, and hire masters of mint, and set your minting slider just high enough that you're burning away 0.01 points of inflation. The tool tip over your current money on the top bar should give you an overview of your monthly and yearly income. Your can be losing money on a monthly basis and still come out in the black if at the end of the year, your income is positive due to end of year taxes.
Join a Trade League. Either the Lubeckian League, or the Venetian League. The League of Venice tends to be the most valuable early on. but Lubeck usually develops strongly early on unless it's annexed. being part of a league means that other members of the league won't compete with you unless they've already out competed all other non-league members, and means that your merchant compete is set to that of the League Leader, if it's better than yours, and it probably is. Since The Hansa is usually a one Province Minor prone to be annexed, Venice is always a good bet.